Millimetre of mercury

A millimetre of mercury is a manometric unit of pressure, formerly defined as the extra pressure generated by a column of mercury one millimetre high, and currently defined as exactly 133.322387415 pascals[1] or exactly 133.322 pascals.[2] It is denoted mmHg[3] or mm Hg.[4][2]

millimetre of mercury
Unit ofPressure
SymbolmmHgormm Hg
1 mmHg in ...... is equal to ...
   SI units   133.322 Pa
   English Engineering units   0.01933678 lbf/in2
Mercury barometer

Although not an SI unit, the millimetre of mercury is still routinely used in medicine, meteorology, aviation, and many other scientific fields.

One millimetre of mercury is approximately 1 Torr, which is 1/760 of standard atmospheric pressure (101325/760  133.322368 pascals). Although the two units are not equal, the relative difference (less than 0.000015%) is negligible for most practical uses.

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