Convert Millimeters of Mercury to Torr

The Millimeters of Mercury (symbol: mmHg) is a unit of pressure. A unit of pressure historically defined as the pressure exerted by a column of mercury exactly 1 millimeter tall at the standard acceleration of gravity (9.80665 m/s²) and the standard density of mercury (13,595.1 kg/m³ at 0 °C). The mmHg's contemporary definition rounds to exactly 133.322387415 Pa (NIST SP 811). Despite being non-SI, mmHg remains the international clinical standard for blood pressure measurement ("120 over 80" mmHg) per WHO and ESH guidelines, and is the default unit for intraocular pressure in ophthalmology (normal IOP 10-21 mmHg per Glaucoma Research Foundation) and intracranial pressure monitoring in neurology. Numerically the mmHg is almost identical to the torr (1 mmHg ≈ 1.0000007 torr — the difference is whether one uses the conventional density or the experimentally measured density of mercury). Barometric atmospheric pressure was historically quoted in mmHg before kPa/hPa adoption (760 mmHg = 1 atm = 101.325 kPa).

It belongs to the metric measurement system.

Millimeters of Mercury are commonly used in tire inflation, weather reporting, scuba diving, and engineering.

The Torr (symbol: torr) is a unit of pressure. A unit of pressure defined as exactly 1/760 of a standard atmosphere (≈ 133.322 Pa). Named after 17th-century physicist Evangelista Torricelli, who in 1643 invented the mercury barometer while studying why suction-lift pumps fail above ~10 m — establishing that the atmosphere itself has weight. The torr is the primary unit in modern vacuum technology and semiconductor fabrication: a "rough vacuum" is ~1 torr, "medium vacuum" 10⁻³ torr (typical of mechanical-pump-only systems), "high vacuum" 10⁻⁶ torr (achievable with turbomolecular pumps, used in mass spectrometry and electron microscopy), and "ultrahigh vacuum" (UHV) 10⁻⁹ torr or lower (semiconductor MBE, surface science, particle accelerators). Manufacturing fabs quote chamber pressures in torr or mTorr (10⁻³ torr) at every process step. Numerically the torr is almost identical to the mmHg (1 torr ≈ 1.000000 mmHg under modern definitions; historically they differed by 0.000015%).

Torr are commonly used in tire inflation, weather reporting, scuba diving, and engineering.