mmHg to atm Conversion Calculator

Formula

How this is calculated

The millimeter of mercury (mmHg) is a historical pressure unit defined as the pressure exerted by a 1 mm column of liquid mercury at 0 °C under standard gravity (9.80665 m/s²). By international convention, 1 standard atmosphere equals exactly 760 mmHg — a definition adopted from early barometry and preserved in the SI system as an exact conventional value.

Because 1 atm = 101,325 Pa and 1 atm = 760 mmHg, each mmHg equals 101 325/760 ≈ 133.322 Pa exactly. Dividing your mmHg value by 760 yields atmospheres; multiplying by 133.322 yields pascals. The Torr, defined as exactly 1/760 atm, differs from 1 mmHg by less than 0.002% and the two units are interchangeable for all practical purposes outside precision metrology.

mmHg remains the standard clinical unit for blood pressure (normal systolic ≈ 120 mmHg, diastolic ≈ 80 mmHg), intraocular pressure (normal range 10–20 mmHg), and many vacuum-gauge applications. Barometric pressure at sea level is ≈ 760 mmHg (1 atm), dropping by roughly 25 mmHg per 300 m of altitude. These conversions assume standard gravity and a standard mercury density; for precision manometry, the exact mercury temperature must be accounted for.