Inch of mercury

From Glossary of Meteorology
(Redirected from Millimeter of mercury)

inch of mercury

A common unit used in the measurement of atmospheric pressure.

1) One inch of mercury (in Hg) is defined as that pressure exerted by a 1-in. column of mercury at standard gravity and a temperature of 0°C:
This is a unit recommended for meteorological use.

2) One 45° inch of mercury [in Hg (45°)] is defined as that pressure exerted by a 1-in. column of mercury at 45° latitude at sea level and a temperature of 0°C.

It is evident that for most purposes these two units are interchangeable. When this is not the case, the unit should be carefully specified. Metric, rather than the English, units of length are used in many branches of science, and in other parts of the world. The early development and continued widespread use of the mercury barometer has fostered this manner of expressing atmospheric pressure. Although it has largely been replaced by the hectopascal (hPa) in most meteorological work, inches of mercury is still used in altimetry, and it remains the most common form of barometer scale calibration.

Copyright 2022 American Meteorological Society (AMS). For permission to reuse any portion of this work, please contact [email protected]. Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act (17 U.S. Code § 107) or that satisfies the conditions specified in Section 108 of the U.S.Copyright Act (17 USC § 108) does not require AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a website or in a searchable database, or other uses of this material, except as exempted by the above statement, require written permission or a license from AMS. Additional details are provided in the AMS Copyright Policy statement.