mmHg to Atmospheres Converter
Convert millimetres of mercury to atmospheres — 760 mmHg is one atmosphere, the original definition. Results update as you type; exact factors shown.
One millimetre of mercury is 0.0013 standard atmospheres — see the exact factor, not a rounded rule of thumb.
How the mmhg to atmospheres converter works
Pressures convert through the pascal (1 N/m²). One bar is exactly 100 kPa; a standard atmosphere is exactly 101.325 kPa; 1 psi is 6.894757 kPa (a pound-force on a square inch); 1 mmHg is 133.322 Pa by the conventional definition.
The UK is metric for most trade and science but keeps miles, pints, stone and mpg (with the imperial gallon) in daily life.
Common pressure conversions
| From | To | Units |
|---|---|---|
| 80 mmHg | 0.1053 atm | millimetre of mercurys to standard atmospheres |
| 100 mmHg | 0.1316 atm | millimetre of mercurys to standard atmospheres |
| 120 mmHg | 0.1579 atm | millimetre of mercurys to standard atmospheres |
| 200 mmHg | 0.2632 atm | millimetre of mercurys to standard atmospheres |
| 300 mmHg | 0.3947 atm | millimetre of mercurys to standard atmospheres |
| 400 mmHg | 0.5263 atm | millimetre of mercurys to standard atmospheres |
| 500 mmHg | 0.6579 atm | millimetre of mercurys to standard atmospheres |
| 600 mmHg | 0.7895 atm | millimetre of mercurys to standard atmospheres |
| 700 mmHg | 0.9211 atm | millimetre of mercurys to standard atmospheres |
| 760 mmHg | 1 atm | millimetre of mercurys to standard atmospheres |
| 1,000 mmHg | 1.3158 atm | millimetre of mercurys to standard atmospheres |
| 1,520 mmHg | 2 atm | millimetre of mercurys to standard atmospheres |
Units in this converter and their exact factors
| Unit | Symbol | One unit in pascals |
|---|---|---|
| pascal | Pa | 1 pascal |
| kilopascal | kPa | 1,000 pascal |
| megapascal | MPa | 1,000,000 pascal |
| bar | bar | 100,000 pascal |
| millibar (hectopascal) | mbar | 100 pascal |
| standard atmosphere | atm | 101,325 pascal |
| pound per square inch | psi | 6,894.757293168 pascal |
| millimetre of mercury | mmHg | 133.322387415 pascal |
| inch of mercury | inHg | 3,386.389 pascal |
FAQFrequently asked questions about pressure conversion
How many mmHg in one atmosphere?
760 mmHg — that was how the atmosphere was first defined, from Torricelli’s barometer.
What is 120 mmHg in atm?
0.158 atm.
Why 760?
Because a mercury column 760 mm tall exerts the same pressure as the atmosphere at sea level, which is what Torricelli measured in 1643.
What is 380 mmHg?
Half an atmosphere — the pressure at roughly 5,500 m altitude.
Do labs still use mmHg?
Vacuum work often does, usually as torr; SI pressure work uses pascals.
Where these figures come from
- BIPM — The International System of Units (SI Brochure, 9th edition) — definitions of the base and derived units.
- NIST Special Publication 811 — Guide for the Use of the International System of Units — the exact conversion factors used here.
- National Physical Laboratory (NPL) — United Kingdom's national measurement authority.
Last checked: September 2026. Conversion factors are fixed by definition and do not change with tax years or regulations.