Convert Torr to Atmosphere (Torr → atm)

Converting torr to atmospheres is straightforward: multiply by the conversion factor. Follow these three steps to do it by hand or in your head.

1. 1
   Take your value in torr

   Start with the number of torr (Torr) you want to convert.
2. 2
   Multiply by 0.001316

   The conversion factor from Torr to atm is 0.001316. Multiply your value by this number.
3. 3
   Read the result in atmospheres

   The result is your value in atmospheres (atm).

Multiply the value in torr by 0.001316. For the reverse direction, multiply by 760.

• ✓1 Torr ≈ 1 mmHg (differ by ~1 ppm — negligible in practice).
• ✓1 atm = 760 Torr exactly.
• ✓Named after Evangelista Torricelli, inventor of the barometer.

• ✗Assuming torr and mmHg are truly identical — they differ by ~10⁻⁷; only matters in metrology.
• ✗Using Torr in everyday context — obscure outside vacuum engineering.
• ✗Mixing Torr and mTorr without specification.

What is the Torr?

The torr equals approximately 1.0000003 mmHg (essentially identical, 133.322 Pa) and is named after Italian physicist Evangelista Torricelli (1608–1647), who invented the mercury barometer. The torr is widely used in vacuum-system specifications, laboratory instruments, and high-vacuum physics. Vacuum levels are categorized: 'low vacuum' is 760 to 1 torr, 'medium vacuum' 1 to 10⁻³ torr, 'high vacuum' below 10⁻³ torr. Mass spectrometers, electron microscopes, and semiconductor manufacturing systems require high vacuum (10⁻⁶ to 10⁻⁹ torr). The torr relates to the mmHg (essentially equal), the pascal (1 torr ≈ 133.3 Pa), the millibar (1 torr ≈ 1.333 mbar), and the atmosphere (760 torr = 1 atm). Modern scientific publications increasingly use the pascal, but the torr remains entrenched in vacuum technology.

• Vacuum-chamber pressure readings
• Semiconductor manufacturing
• Older physics literature

What is the Atmosphere?

The atmosphere equals exactly 101,325 pascals (the average atmospheric pressure at sea level, latitude 45°) and is a reference unit in chemistry, diving, and engineering. Defined for scientific convenience to represent 'standard atmospheric pressure,' it is widely used in chemistry (gas laws, reaction conditions), aviation (cabin pressure relative to ambient), and scuba diving (depth pressure: every 10 m of seawater adds about 1 atm). Standard reference conditions in chemistry often specify 1 atm and 25°C. The atmosphere relates to the pascal (101,325 Pa = 1 atm), the kilopascal (101.325 kPa = 1 atm), the bar (1.01325 bar = 1 atm), the psi (14.696 psi = 1 atm), the torr (760 torr = 1 atm), and the meter of seawater (10.33 mH₂O = 1 atm). The 'technical atmosphere' (1 at = 98.066 kPa = 1 kgf/cm²) is a slightly different historical unit no longer in use.

• Chemistry standard conditions
• Aviation cockpit pressurisation references
• Pressure tank and vessel ratings