**Full name:**

**Plural form:** millimeters mercury

**Symbol:** mm Hg

**Alternate spelling:** mm mercury

**Category type:** pressure

**Scale factor:** 133.322387415

The SI derived unit for pressure is the pascal.

1 pascal is equal to 0.0075006157584566 millimeter mercury.

Valid units must be of the **pressure** type.

You can use this form to select from known units:

The millimeter of mercury by definition is 133.322387415 Pa (13.5951 g/cm3 × 9.80665 m/s2 × 1 mm), which is approximated with known accuracies of density of mercury and standard gravity.

The torr is defined as 1/760 of one standard atmosphere, while the atmosphere is defined as 101325 pascals. Therefore, 1 Torr is equal to

101325/760 Pa. The decimal form of this fraction is approximately 133.322368421.

The relationship between the torr and the millimeter of mercury is:

1 Torr = 0.999999857533699 mmHg

1 mmHg = 1.000000142466321 Torr

The difference between one millimeter of mercury and one torr, as well as between one atmosphere (101.325 kPa) and 760 mmHg (101.3250144354 kPa), is less than one part in seven million (or less than 0.000015%). This small difference is negligible for most applications outside metrology.

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