millimeter of mercury
Pressureexact by definition
The millimetre of mercury is the pressure exerted by a one millimetre column of mercury of conventional density 13 595.1 kg/m³ under standard gravity, which gives exactly 133.322387415 pascals. The value is exact given that convention, but the convention is itself an idealisation: real mercury changes density with temperature, so a working barometer needs a temperature correction.
Watch out: The torr and the millimetre of mercury are not identical. The torr is defined as exactly 1/760 of a standard atmosphere, or 133.3223684... Pa, while mmHg is 133.322387415 Pa. They differ by about one part in seven million, which is irrelevant for blood pressure and can matter in precision vacuum metrology.
| 1 | 0.13332239 |
The unit descends directly from Torricelli's 1643 mercury barometer, in which atmospheric pressure supported a column about 760 mm tall. Medicine adopted it for blood pressure and has never left.
One millimeter of mercury in every pressure unit
| 1,333.22 | microbar (μbar) | |
| 1,333.22 | barye (Ba) | |
| 1,000 | millitorr (mTorr) | |
| 133.322 | pascal (Pa) | convert → |
| 13.5951 | millimeter of water column (mmH₂O) | |
| 2.7845 | pound per square foot (lb/ft²) | |
| 1.35951 | centimeter of water column (cmH₂O) | |
| 1.33322 | hectopascal (hPa) | |
| 1.33322 | millibar (mbar) | |
| 1 | torr (Torr) | |
| 1 | millimeter of mercury (mmHg)this unit | |
| 0.53524 | inch of water column (in w.g.) | convert → |
| 0.133322 | kilopascal (kPa) | convert → |
| 0.0446033 | foot of water column (ft H₂O) | convert → |
| 0.0393701 | inch of mercury (inHg) | convert → |
| 0.0193368 | pound per square inch (psi) | convert → |
| 0.0135951 | meter of water column (m H₂O) | |
| 0.0133322 | decibar (dbar) | |
| 0.00135951 | kilogram-force per square centimeter (kgf/cm²) | |
| 0.00133322 | bar (bar) | convert → |
| 0.00131579 | atmosphere (atm) | convert → |
| 0.000133322 | megapascal (MPa) | convert → |
| 0.0000193368 | kip per square inch (ksi) | |
| 1.33322e-07 | gigapascal (GPa) | |
| 1.93368e-08 | million pounds per square inch (Mpsi) |