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Available in 20 languages" > <label id="p-lang-btn-label" for="p-lang-btn-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--action-progressive mw-portlet-lang-heading-20" aria-hidden="true" ><span class="vector-icon mw-ui-icon-language-progressive mw-ui-icon-wikimedia-language-progressive"></span> <span class="vector-dropdown-label-text">20 languages</span> </label> <div class="vector-dropdown-content"> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li class="interlanguage-link interwiki-ca mw-list-item"><a href="https://ca.wikipedia.org/wiki/Polzada_de_mercuri" title="Polzada de mercuri – Catalan" lang="ca" hreflang="ca" data-title="Polzada de mercuri" data-language-autonym="Català" data-language-local-name="Catalan" class="interlanguage-link-target"><span>Català</span></a></li><li class="interlanguage-link interwiki-cs mw-list-item"><a href="https://cs.wikipedia.org/wiki/Palec_rtu%C5%A5ov%C3%A9ho_sloupce" title="Palec rtuťového sloupce – Czech" lang="cs" hreflang="cs" data-title="Palec rtuťového sloupce" data-language-autonym="Čeština" data-language-local-name="Czech" class="interlanguage-link-target"><span>Čeština</span></a></li><li class="interlanguage-link interwiki-de badge-Q70894304 mw-list-item" title=""><a href="https://de.wikipedia.org/wiki/Zoll_Quecksilber" title="Zoll Quecksilber – German" lang="de" hreflang="de" data-title="Zoll Quecksilber" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target"><span>Deutsch</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Pulgada_de_mercurio" title="Pulgada de mercurio – Spanish" lang="es" hreflang="es" data-title="Pulgada de mercurio" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-fa mw-list-item"><a href="https://fa.wikipedia.org/wiki/%D8%A7%DB%8C%D9%86%DA%86_%D8%AC%DB%8C%D9%88%D9%87" title="اینچ جیوه – Persian" lang="fa" hreflang="fa" data-title="اینچ جیوه" data-language-autonym="فارسی" data-language-local-name="Persian" class="interlanguage-link-target"><span>فارسی</span></a></li><li class="interlanguage-link interwiki-fr mw-list-item"><a href="https://fr.wikipedia.org/wiki/Pouce_de_mercure" title="Pouce de mercure – French" lang="fr" hreflang="fr" data-title="Pouce de mercure" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/%EC%88%98%EC%9D%80%EC%A3%BC_%EC%9D%B8%EC%B9%98" title="수은주 인치 – Korean" lang="ko" hreflang="ko" data-title="수은주 인치" data-language-autonym="한국어" data-language-local-name="Korean" class="interlanguage-link-target"><span>한국어</span></a></li><li class="interlanguage-link interwiki-hi mw-list-item"><a href="https://hi.wikipedia.org/wiki/%E0%A4%AA%E0%A4%BE%E0%A4%B0%E0%A5%87_%E0%A4%95%E0%A4%BE_%E0%A4%87%E0%A4%82%E0%A4%9A" title="पारे का इंच – Hindi" lang="hi" hreflang="hi" data-title="पारे का इंच" data-language-autonym="हिन्दी" data-language-local-name="Hindi" class="interlanguage-link-target"><span>हिन्दी</span></a></li><li class="interlanguage-link interwiki-id mw-list-item"><a href="https://id.wikipedia.org/wiki/Inci_raksa" title="Inci raksa – Indonesian" lang="id" hreflang="id" data-title="Inci raksa" data-language-autonym="Bahasa Indonesia" data-language-local-name="Indonesian" class="interlanguage-link-target"><span>Bahasa Indonesia</span></a></li><li class="interlanguage-link interwiki-it mw-list-item"><a href="https://it.wikipedia.org/wiki/InHg" title="InHg – Italian" lang="it" hreflang="it" data-title="InHg" data-language-autonym="Italiano" data-language-local-name="Italian" class="interlanguage-link-target"><span>Italiano</span></a></li><li class="interlanguage-link interwiki-ms mw-list-item"><a href="https://ms.wikipedia.org/wiki/Inci_merkuri" title="Inci merkuri – Malay" lang="ms" hreflang="ms" data-title="Inci merkuri" data-language-autonym="Bahasa Melayu" data-language-local-name="Malay" class="interlanguage-link-target"><span>Bahasa Melayu</span></a></li><li class="interlanguage-link interwiki-ja mw-list-item"><a href="https://ja.wikipedia.org/wiki/%E6%B0%B4%E9%8A%80%E6%9F%B1%E3%82%A4%E3%83%B3%E3%83%81" title="水銀柱インチ – Japanese" lang="ja" hreflang="ja" data-title="水銀柱インチ" data-language-autonym="日本語" data-language-local-name="Japanese" class="interlanguage-link-target"><span>日本語</span></a></li><li class="interlanguage-link interwiki-no mw-list-item"><a href="https://no.wikipedia.org/wiki/Tommer_kvikks%C3%B8lv" title="Tommer kvikksølv – Norwegian Bokmål" lang="nb" hreflang="nb" data-title="Tommer kvikksølv" data-language-autonym="Norsk bokmål" data-language-local-name="Norwegian Bokmål" class="interlanguage-link-target"><span>Norsk bokmål</span></a></li><li class="interlanguage-link interwiki-pt mw-list-item"><a href="https://pt.wikipedia.org/wiki/Polegada_de_merc%C3%BArio" title="Polegada de mercúrio – Portuguese" lang="pt" hreflang="pt" data-title="Polegada de mercúrio" data-language-autonym="Português" data-language-local-name="Portuguese" class="interlanguage-link-target"><span>Português</span></a></li><li class="interlanguage-link interwiki-ru mw-list-item"><a href="https://ru.wikipedia.org/wiki/%D0%94%D1%8E%D0%B9%D0%BC_%D1%80%D1%82%D1%83%D1%82%D0%BD%D0%BE%D0%B3%D0%BE_%D1%81%D1%82%D0%BE%D0%BB%D0%B1%D0%B0" title="Дюйм ртутного столба – Russian" lang="ru" hreflang="ru" data-title="Дюйм ртутного столба" data-language-autonym="Русский" data-language-local-name="Russian" class="interlanguage-link-target"><span>Русский</span></a></li><li class="interlanguage-link interwiki-simple mw-list-item"><a href="https://simple.wikipedia.org/wiki/Inch_of_mercury" title="Inch of mercury – Simple English" lang="en-simple" hreflang="en-simple" data-title="Inch of mercury" data-language-autonym="Simple English" data-language-local-name="Simple English" class="interlanguage-link-target"><span>Simple English</span></a></li><li class="interlanguage-link interwiki-sv mw-list-item"><a href="https://sv.wikipedia.org/wiki/InHg" title="InHg – Swedish" lang="sv" hreflang="sv" data-title="InHg" data-language-autonym="Svenska" data-language-local-name="Swedish" class="interlanguage-link-target"><span>Svenska</span></a></li><li class="interlanguage-link interwiki-ta mw-list-item"><a href="https://ta.wikipedia.org/wiki/%E0%AE%AA%E0%AE%BE%E0%AE%A4%E0%AE%B0%E0%AE%9A_%E0%AE%85%E0%AE%99%E0%AF%8D%E0%AE%95%E0%AF%81%E0%AE%B2%E0%AE%AE%E0%AF%8D" title="பாதரச அங்குலம் – Tamil" lang="ta" hreflang="ta" data-title="பாதரச அங்குலம்" data-language-autonym="தமிழ்" data-language-local-name="Tamil" class="interlanguage-link-target"><span>தமிழ்</span></a></li><li class="interlanguage-link interwiki-vi mw-list-item"><a href="https://vi.wikipedia.org/wiki/Inch_th%E1%BB%A7y_ng%C3%A2n" title="Inch thủy ngân – Vietnamese" lang="vi" hreflang="vi" data-title="Inch thủy ngân" data-language-autonym="Tiếng Việt" data-language-local-name="Vietnamese" class="interlanguage-link-target"><span>Tiếng Việt</span></a></li><li class="interlanguage-link interwiki-zh mw-list-item"><a href="https://zh.wikipedia.org/wiki/%E8%8B%B1%E5%AF%B8%E6%B1%9E%E6%9F%B1" title="英寸汞柱 – Chinese" lang="zh" hreflang="zh" data-title="英寸汞柱" data-language-autonym="中文" data-language-local-name="Chinese" class="interlanguage-link-target"><span>中文</span></a></li> </ul> <div class="after-portlet after-portlet-lang"><span class="wb-langlinks-edit wb-langlinks-link"><a href="https://www.wikidata.org/wiki/Special:EntityPage/Q1050958#sitelinks-wikipedia" title="Edit 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data-mw-deduplicate="TemplateStyles:r1236090951">.mw-parser-output .hatnote{font-style:italic}.mw-parser-output div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}@media print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}</style><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/wiki/Inch_of_water" title="Inch of water">Inch of water</a></div> <style data-mw-deduplicate="TemplateStyles:r1251242444">.mw-parser-output .ambox{border:1px solid #a2a9b1;border-left:10px solid #36c;background-color:#fbfbfb;box-sizing:border-box}.mw-parser-output .ambox+link+.ambox,.mw-parser-output .ambox+link+style+.ambox,.mw-parser-output .ambox+link+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+style+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+link+.ambox{margin-top:-1px}html body.mediawiki .mw-parser-output .ambox.mbox-small-left{margin:4px 1em 4px 0;overflow:hidden;width:238px;border-collapse:collapse;font-size:88%;line-height:1.25em}.mw-parser-output .ambox-speedy{border-left:10px solid #b32424;background-color:#fee7e6}.mw-parser-output .ambox-delete{border-left:10px solid #b32424}.mw-parser-output .ambox-content{border-left:10px solid #f28500}.mw-parser-output .ambox-style{border-left:10px solid #fc3}.mw-parser-output .ambox-move{border-left:10px solid #9932cc}.mw-parser-output .ambox-protection{border-left:10px solid #a2a9b1}.mw-parser-output .ambox .mbox-text{border:none;padding:0.25em 0.5em;width:100%}.mw-parser-output .ambox .mbox-image{border:none;padding:2px 0 2px 0.5em;text-align:center}.mw-parser-output .ambox .mbox-imageright{border:none;padding:2px 0.5em 2px 0;text-align:center}.mw-parser-output .ambox .mbox-empty-cell{border:none;padding:0;width:1px}.mw-parser-output .ambox .mbox-image-div{width:52px}@media(min-width:720px){.mw-parser-output .ambox{margin:0 10%}}@media print{body.ns-0 .mw-parser-output .ambox{display:none!important}}</style><table class="box-More_citations_needed plainlinks metadata ambox ambox-content ambox-Refimprove" role="presentation"><tbody><tr><td class="mbox-image"><div class="mbox-image-div"><span typeof="mw:File"><a href="/wiki/File:Question_book-new.svg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/50px-Question_book-new.svg.png" decoding="async" width="50" height="39" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/75px-Question_book-new.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/100px-Question_book-new.svg.png 2x" data-file-width="512" data-file-height="399" /></a></span></div></td><td class="mbox-text"><div class="mbox-text-span">This article <b>needs additional citations for <a href="/wiki/Wikipedia:Verifiability" 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Unsourced material may be challenged and removed.<br /><small><span class="plainlinks"><i>Find sources:</i> <a rel="nofollow" class="external text" href="https://www.google.com/search?as_eq=wikipedia&q=%22Inch+of+mercury%22">"Inch of mercury"</a> – <a rel="nofollow" class="external text" href="https://www.google.com/search?tbm=nws&q=%22Inch+of+mercury%22+-wikipedia&tbs=ar:1">news</a> <b>·</b> <a rel="nofollow" class="external text" href="https://www.google.com/search?&q=%22Inch+of+mercury%22&tbs=bkt:s&tbm=bks">newspapers</a> <b>·</b> <a rel="nofollow" class="external text" href="https://www.google.com/search?tbs=bks:1&q=%22Inch+of+mercury%22+-wikipedia">books</a> <b>·</b> <a rel="nofollow" class="external text" href="https://scholar.google.com/scholar?q=%22Inch+of+mercury%22">scholar</a> <b>·</b> <a rel="nofollow" class="external text" href="https://www.jstor.org/action/doBasicSearch?Query=%22Inch+of+mercury%22&acc=on&wc=on">JSTOR</a></span></small></span> <span 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div:not(.notheme){background:#1f1f23!important;color:#f8f9fa}}@media(min-width:640px){body.skin--responsive .mw-parser-output .infobox-table{display:table!important}body.skin--responsive .mw-parser-output .infobox-table>caption{display:table-caption!important}body.skin--responsive .mw-parser-output .infobox-table>tbody{display:table-row-group}body.skin--responsive .mw-parser-output .infobox-table tr{display:table-row!important}body.skin--responsive .mw-parser-output .infobox-table th,body.skin--responsive .mw-parser-output .infobox-table td{padding-left:inherit;padding-right:inherit}}</style><table class="infobox ib-unit"><tbody><tr><th colspan="2" class="infobox-above">Inch of mercury</th></tr><tr><td colspan="2" class="infobox-image notheme" style="background-color: #f8f9fa;"><span class="mw-default-size" typeof="mw:File/Frameless"><a href="/wiki/File:Rare_American_Barometer,_Lyman_King,_Clifton_Springs,_New_York,_c._1860_-_Museum_of_Science_and_Industry_(Chicago)_-_DSC06342.JPG" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/d/df/Rare_American_Barometer%2C_Lyman_King%2C_Clifton_Springs%2C_New_York%2C_c._1860_-_Museum_of_Science_and_Industry_%28Chicago%29_-_DSC06342.JPG/220px-Rare_American_Barometer%2C_Lyman_King%2C_Clifton_Springs%2C_New_York%2C_c._1860_-_Museum_of_Science_and_Industry_%28Chicago%29_-_DSC06342.JPG" decoding="async" width="220" height="616" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/d/df/Rare_American_Barometer%2C_Lyman_King%2C_Clifton_Springs%2C_New_York%2C_c._1860_-_Museum_of_Science_and_Industry_%28Chicago%29_-_DSC06342.JPG/330px-Rare_American_Barometer%2C_Lyman_King%2C_Clifton_Springs%2C_New_York%2C_c._1860_-_Museum_of_Science_and_Industry_%28Chicago%29_-_DSC06342.JPG 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/d/df/Rare_American_Barometer%2C_Lyman_King%2C_Clifton_Springs%2C_New_York%2C_c._1860_-_Museum_of_Science_and_Industry_%28Chicago%29_-_DSC06342.JPG/440px-Rare_American_Barometer%2C_Lyman_King%2C_Clifton_Springs%2C_New_York%2C_c._1860_-_Museum_of_Science_and_Industry_%28Chicago%29_-_DSC06342.JPG 2x" data-file-width="1960" data-file-height="5490" /></a></span><div class="infobox-caption">Early American barometer calibrated in inches of mercury</div></td></tr><tr><th colspan="2" class="infobox-header">General information</th></tr><tr><th scope="row" class="infobox-label">Unit of</th><td class="infobox-data"><a href="/wiki/Pressure" title="Pressure">Pressure</a></td></tr><tr><th scope="row" class="infobox-label">Symbol</th><td class="infobox-data">inHg, ″Hg</td></tr><tr><th colspan="2" class="infobox-header">Conversions </th></tr><tr class="nowrap"><td>1 inHg <i>in ...</i></td><td><i>... is equal to ...</i></td></tr><tr style="display:none"><th colspan="2"> </th></tr><tr><th scope="row" class="infobox-label"><span class="nowrap">   </span><a href="/wiki/SI_units" class="mw-redirect" title="SI units">SI units</a></th><td class="infobox-data"><span class="nowrap">   </span>3.38639 <a href="/wiki/Pascal_(unit)" title="Pascal (unit)">kPa</a></td></tr><tr><th scope="row" class="infobox-label"><span class="nowrap">   </span><a href="/wiki/United_States_customary_units" title="United States customary units">United States customary units</a></th><td class="infobox-data"><span class="nowrap">   </span>0.491154 <a href="/wiki/Pound_per_square_inch" title="Pound per square inch">psi</a></td></tr></tbody></table><style data-mw-deduplicate="TemplateStyles:r1236303919">@media screen{html.skin-theme-clientpref-night .mw-parser-output .infobox-has-images-with-white-backgrounds img{background:white}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .infobox-has-images-with-white-backgrounds img{background:white}}</style> <p><b>Inch of mercury</b> (<b>inHg</b> and <b>″Hg</b>) is a non-<a href="/wiki/SI" class="mw-redirect" title="SI">SI</a> <a href="/wiki/Unit_of_measurement" title="Unit of measurement">unit of measurement</a> for <a href="/wiki/Pressure" title="Pressure">pressure</a>. It is used for <a href="/wiki/Barometric_pressure" class="mw-redirect" title="Barometric pressure">barometric pressure</a> in <a href="/wiki/Weather_forecasting" title="Weather forecasting">weather reports</a>, <a href="/wiki/Refrigeration" title="Refrigeration">refrigeration</a> and <a href="/wiki/Aviation" title="Aviation">aviation</a> in the <a href="/wiki/United_States_customary_units" title="United States customary units">United States</a>. </p><p>It is the pressure exerted by a column of <a href="/wiki/Mercury_(element)" title="Mercury (element)">mercury</a> 1 inch (25.4 mm) in height at the <a href="/wiki/Standard_gravity" title="Standard gravity">standard acceleration of gravity</a>. Conversion to metric units depends on the density of mercury, and hence its temperature; typical conversion factors are:<sup id="cite_ref-NIST811_1-0" class="reference"><a href="#cite_note-NIST811-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> </p> <table class="wikitable"> <tbody><tr> <th>Conditions </th> <th>Pressure </th></tr> <tr> <td>conventional </td> <td>3386.389 pascals </td></tr> <tr> <td>32 °F (0 °C) </td> <td>3386.38 pascals </td></tr> <tr> <td>60 °F (16 °C) </td> <td>3376.85 pascals </td></tr></tbody></table> <p>In older literature, an "inch of mercury" is based on the height of a column of mercury at 60 °F (15.6 °C).<sup id="cite_ref-NIST811_1-1" class="reference"><a href="#cite_note-NIST811-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> </p> <dl><dd>1 inHg<sub>60 °F</sub> = 3,376.85 pascals (33.7685 hPa)</dd></dl> <p>In Imperial units: 1 inHg<sub>60 °F</sub> = 0.489 771 <a href="/wiki/Pounds_per_square_inch" class="mw-redirect" title="Pounds per square inch">psi</a>, or 2.041 771 inHg<sub>60 °F</sub> = 1 psi. </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="Applications">Applications</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Inch_of_mercury&action=edit&section=1" title="Edit section: Applications"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <div class="mw-heading mw-heading3"><h3 id="Aircraft_and_automobiles">Aircraft and automobiles</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Inch_of_mercury&action=edit&section=2" title="Edit section: Aircraft and automobiles"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Aircraft <a href="/wiki/Altimeter" title="Altimeter">altimeters</a> measure the relative pressure difference between the lower ambient pressure at altitude and a calibrated reading on the ground. In the United States, Canada<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> and Japan, these altimeter readings are provided in inches of mercury, but most other nations use <a href="/wiki/Hectopascal" class="mw-redirect" title="Hectopascal">hectopascals</a>. Ground readings vary with weather and along the route of the aircraft as it travels, so current readings are relayed periodically by air traffic control. Aircraft operating at higher altitudes (at or above what is called the <a href="/wiki/Flight_level#Transition_altitude" title="Flight level">transition altitude</a>, which varies by country) set their barometric <a href="/wiki/Altimeter" title="Altimeter">altimeters</a> to a standard pressure of 29.92 inHg (1 atm = 29.92 inHg) or 1013.25 <a href="/wiki/Pascal_(unit)" title="Pascal (unit)">hPa</a> (1 hPa = 1 <a href="/wiki/Mbar" class="mw-redirect" title="Mbar">mbar</a>) regardless of the actual sea level pressure. The resulting altimeter readings are known as <a href="/wiki/Flight_level" title="Flight level">flight levels</a>. </p><p><a href="/wiki/Piston_engine" class="mw-redirect" title="Piston engine">Piston engine</a> <a href="/wiki/Aircraft" title="Aircraft">aircraft</a> with <a href="/wiki/Constant-speed_propeller" class="mw-redirect" title="Constant-speed propeller">constant-speed propellers</a> also use inches of mercury to measure <a href="/wiki/Manifold_pressure" class="mw-redirect" title="Manifold pressure">manifold pressure</a>, which is indicative of engine power produced in engines equipped with a <a href="/wiki/Supercharger" title="Supercharger">supercharger</a> or <a href="/wiki/Turbocharger" title="Turbocharger">turbosupercharger</a> (naturally aspirated engines measure manifold vacuum instead). In automobile racing, particularly <a href="/wiki/United_States_Auto_Club" title="United States Auto Club">United States Auto Club</a> and <a href="/wiki/Champ_Car" class="mw-redirect" title="Champ Car">Champ Car</a> <a href="/wiki/Indy_car_racing" class="mw-redirect" title="Indy car racing">Indy car racing</a>, inches of mercury was the unit used to measure <a href="/wiki/Turbocharger" title="Turbocharger">turbocharger</a> inlet pressure. However, the inch of mercury is still used today in car performance modification to measure the amount of vacuum or pressure within the engine's intake manifold. This can be seen on "boost gauges (forced induction) or vacuum gauges (natural induction), which give a rough indication of the relative power being produced at any given time. </p> <div class="mw-heading mw-heading3"><h3 id="Cooling_systems">Cooling systems</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Inch_of_mercury&action=edit&section=3" title="Edit section: Cooling systems"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>In <a href="/wiki/Air_conditioning" title="Air conditioning">air conditioning</a> and refrigeration, inHg is often used to describe "inches of mercury vacuum", or pressures below ambient atmospheric pressure, for recovery of refrigerants from air conditioning and refrigeration systems, as well as for leak testing of systems while under a vacuum, and for dehydration of refrigeration systems. The low-side gauge in a refrigeration gauge manifold indicates pressures below ambient in "inches of mercury vacuum" (inHg), down to a 30 inHg vacuum. </p><p>Inches of mercury is also used in automotive cooling system vacuum test and fill tools. A technician will use this tool to remove air from modern automotive cooling systems, test the system's ability to hold vacuum, and subsequently refill using the vacuum as suction for the new coolant. Typical minimum vacuum values are between 22 and 27 inHg. </p> <div class="mw-heading mw-heading3"><h3 id="Vacuum_brakes">Vacuum brakes</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Inch_of_mercury&action=edit&section=4" title="Edit section: Vacuum brakes"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Inches of mercury was the usual unit of pressure measurement in railway <a href="/wiki/Vacuum_brake" title="Vacuum brake">vacuum brakes</a>. </p> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Inch_of_mercury&action=edit&section=5" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/Torr" title="Torr">Torr</a> (millimeters of mercury)</li> <li><a href="/wiki/Bar_(unit)" title="Bar (unit)">Bar (unit)</a></li> <li><a href="/wiki/Mercury_barometer" class="mw-redirect" title="Mercury barometer">Mercury barometer</a></li> <li><a href="/wiki/Millimetre_of_mercury" title="Millimetre of mercury">Millimetre of mercury</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Inch_of_mercury&action=edit&section=6" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist"> <div class="mw-references-wrap"><ol class="references"> <li id="cite_note-NIST811-1"><span class="mw-cite-backlink">^ <a href="#cite_ref-NIST811_1-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-NIST811_1-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text">Barry N. Taylor, <i>Guide for the Use of the International System of Units (SI),</i> 1995, <a href="/wiki/NIST" class="mw-redirect" title="NIST">NIST</a> Special Publication 811, Appendix B <a rel="nofollow" class="external autonumber" href="http://physics.nist.gov/Pubs/SP811/appenB8.html#I">[1]</a></span> </li> <li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text">From the Ground Up – 29th Edition <sup class="noprint Inline-Template" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Citing_sources" title="Wikipedia:Citing sources"><span title="Please supply an ISBN for this book.">ISBN missing</span></a></i>]</sup> <sup class="noprint Inline-Template" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Citing_sources" title="Wikipedia:Citing sources"><span title="This citation requires a reference to the specific page or range of pages in which the material appears. (December 2022)">page needed</span></a></i>]</sup></span> </li> </ol></div></div> <div class="navbox-styles"><style data-mw-deduplicate="TemplateStyles:r1129693374">.mw-parser-output .hlist dl,.mw-parser-output .hlist ol,.mw-parser-output .hlist ul{margin:0;padding:0}.mw-parser-output .hlist dd,.mw-parser-output .hlist dt,.mw-parser-output .hlist li{margin:0;display:inline}.mw-parser-output .hlist.inline,.mw-parser-output .hlist.inline dl,.mw-parser-output .hlist.inline ol,.mw-parser-output .hlist.inline ul,.mw-parser-output .hlist dl dl,.mw-parser-output .hlist dl ol,.mw-parser-output .hlist dl ul,.mw-parser-output .hlist ol dl,.mw-parser-output .hlist ol ol,.mw-parser-output .hlist ol ul,.mw-parser-output .hlist ul dl,.mw-parser-output .hlist ul ol,.mw-parser-output .hlist ul ul{display:inline}.mw-parser-output .hlist .mw-empty-li{display:none}.mw-parser-output .hlist dt::after{content:": "}.mw-parser-output .hlist dd::after,.mw-parser-output .hlist li::after{content:" · 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li a abbr{color:var(--color-base)!important}@media(prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}}@media print{.mw-parser-output .navbar{display:none!important}}</style><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:United_States_Customary_Units" title="Template:United States Customary Units"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:United_States_Customary_Units" title="Template talk:United States Customary Units"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:United_States_Customary_Units" title="Special:EditPage/Template:United States Customary Units"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="United_States_customary_units" style="font-size:114%;margin:0 4em"><a href="/wiki/United_States_customary_units" title="United States customary units">United States customary units</a></div></th></tr><tr><td class="navbox-abovebelow" colspan="2"><div><a href="/wiki/Comparison_of_the_imperial_and_US_customary_measurement_systems" title="Comparison of the imperial and US customary measurement systems">Comparison with imperial unit system</a></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Length</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Thousandth_of_an_inch" title="Thousandth of an inch">Thousandth of an inch</a></li> <li><a href="/wiki/Inch" title="Inch">Inch</a></li> <li><a href="/wiki/Hand_(unit)" title="Hand (unit)">Hand</a></li> <li><a href="/wiki/Link_(unit)" title="Link (unit)">Link</a></li> <li><a href="/wiki/Foot_(unit)" title="Foot (unit)">Foot</a></li> <li><a href="/wiki/Yard" title="Yard">Yard</a></li> <li><a href="/wiki/Rod_(unit)" title="Rod (unit)">Rod</a></li> <li><a href="/wiki/Chain_(unit)" title="Chain (unit)">Chain</a></li> <li><a href="/wiki/Furlong" title="Furlong">Furlong</a></li> <li><a href="/wiki/Mile" title="Mile">Mile</a> <ul><li><a href="/wiki/Statute_mile" class="mw-redirect" title="Statute mile">statute</a></li></ul></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Area</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Square_inch" title="Square inch">Square inch</a></li> <li><a href="/wiki/Square_foot" title="Square foot">Square foot</a></li> <li><a href="/wiki/Square_yard" title="Square yard">Square yard</a></li> <li><a href="/wiki/Acre" title="Acre">Acre</a></li> <li><a href="/wiki/Square_mile" title="Square mile">Square mile</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Volume</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%">Derived</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Cubic_inch" title="Cubic inch">Cubic inch</a></li> <li><a href="/wiki/Cubic_foot" title="Cubic foot">Cubic foot</a></li> <li><a href="/wiki/Cubic_yard" title="Cubic yard">Cubic yard</a></li> <li><a href="/wiki/Cubic_mile" title="Cubic mile">Cubic mile</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Cooking</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Teaspoon" title="Teaspoon">Teaspoon</a></li> <li><a href="/wiki/Tablespoon" title="Tablespoon">Tablespoon</a></li> <li><a href="/wiki/Fluid_ounce" title="Fluid ounce">Fluid ounce</a></li> <li><a href="/wiki/Cup_(unit)" title="Cup (unit)">Cup</a></li> <li><a href="/wiki/Pint" title="Pint">Pint</a></li> <li><a href="/wiki/Quart" title="Quart">Quart</a></li> <li><a href="/wiki/Gallon" title="Gallon">Gallon</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Wood</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Board_foot" title="Board foot">Board foot</a></li> <li><a href="/wiki/Cord_(unit)" title="Cord (unit)">Cord</a></li> <li><a href="/wiki/Face_cord" title="Face cord">Face cord</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Other</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Minim_(unit)" title="Minim (unit)">Minim</a></li> <li><a href="/wiki/Gill_(unit)" title="Gill (unit)">Gill</a></li> <li><a href="/wiki/Peck" title="Peck">Peck</a></li> <li><a href="/wiki/Bushel" title="Bushel">Bushel</a></li> <li><a href="/wiki/Barrel_(unit)" title="Barrel (unit)">Barrel</a></li> <li><a href="/wiki/Acre-foot" title="Acre-foot">Acre-foot</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Speed</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Feet_per_second" class="mw-redirect" title="Feet per second">Feet per second</a></li> <li><a href="/wiki/Miles_per_hour" title="Miles per hour">Miles per hour</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Mass</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Grain_(unit)" title="Grain (unit)">Grain</a></li> <li><a href="/wiki/Dram_(unit)" title="Dram (unit)">Dram</a></li> <li><a href="/wiki/Ounce" title="Ounce">Ounce</a></li> <li><a href="/wiki/Pound_(mass)" title="Pound (mass)">Pound</a></li> <li><a href="/wiki/Hundredweight" title="Hundredweight">Hundredweight</a></li> <li><a href="/wiki/Ton" title="Ton">Ton</a> <ul><li><a href="/wiki/Long_ton" title="Long ton">Long</a></li> <li><a href="/wiki/Short_ton" title="Short ton">Short</a></li></ul></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Force</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Poundal" title="Poundal">Poundal</a></li> <li><a href="/wiki/Pound_(force)" title="Pound (force)">Pound-force</a></li> <li><a href="/wiki/Kip_(unit)" title="Kip (unit)">Kip</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Pressure</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a class="mw-selflink selflink">Inch of mercury</a></li> <li><a href="/wiki/Pounds_per_square_inch" class="mw-redirect" title="Pounds per square inch">Pounds per square inch</a></li> <li><a href="/wiki/Ksi_(unit)" class="mw-redirect" title="Ksi (unit)">Kilopounds per square inch</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Other units and measures</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Bolt_(cloth)" title="Bolt (cloth)">Bolt (cloth)</a></li> <li><a href="/wiki/British_thermal_unit" title="British thermal unit">British thermal unit</a></li> <li><a href="/wiki/Degree_(angle)" title="Degree (angle)">Degree (angle)</a></li> <li><a href="/wiki/Fahrenheit" title="Fahrenheit">Fahrenheit</a></li> <li><a href="/wiki/Foot-candle" title="Foot-candle">Foot-candle</a></li> <li><a href="/wiki/Foot-lambert" title="Foot-lambert">Foot-lambert</a></li> <li><a href="/wiki/Foot-pound_(energy)" title="Foot-pound (energy)">Foot-pound (energy)</a></li> <li><a href="/wiki/Horsepower" title="Horsepower">Horsepower</a></li> <li><a href="/wiki/Perm_(unit)" title="Perm (unit)">Perm</a></li> <li><a href="/wiki/Pound-foot_(torque)" title="Pound-foot (torque)">Pound-foot (torque)</a></li> <li><a href="/wiki/Spinning_count" title="Spinning count">Spinning count</a></li> <li><a href="/wiki/Ton_of_refrigeration" title="Ton of refrigeration">Ton of refrigeration</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Related systems</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/American_wire_gauge" title="American wire gauge">American wire gauge</a></li> <li><a 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