Convert Torr to Inches of Mercury

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.

The Inch of Mercury (symbol: inHg) is a unit of pressure. A pressure unit defined as the pressure exerted by a 1-inch column of mercury at the standard density of mercury (0 °C) and the standard acceleration of gravity (≈ 3,386.389 Pa per NIST SP 811). Inches of mercury are the primary unit in US aviation for altimeter settings (the QNH datum is reported in inHg in METAR weather observations — "Altimeter 30.12 inHg" means 30.12 inHg corrected to mean sea level), US barometric weather reporting on consumer indoor weather stations and TV weather graphics, HVAC and refrigeration duct/return static pressure (often quoted as fractions of an inHg, e.g., 0.25 inHg = ~62 Pa), and some legacy automotive vacuum gauges measuring intake-manifold vacuum below atmospheric (a healthy engine reads ~18-22 inHg of vacuum at idle). Standard sea-level atmospheric pressure is 29.92 inHg = 1013.25 hPa = 101.325 kPa.

It belongs to the imperial measurement system.

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