mmHg to Atmospheres Converter
Convert millimeters of mercury to atmospheres — 760 mmHg is one atmosphere, the original definition. Results update as you type; exact factors shown.
One millimeter 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 US uses customary units (US gallon, short ton, °F) in daily life; NIST SP 811 gives the exact SI factors.
Common pressure conversions
| From | To | Units |
|---|---|---|
| 80 mmHg | 0.1053 atm | millimeter of mercurys to standard atmospheres |
| 100 mmHg | 0.1316 atm | millimeter of mercurys to standard atmospheres |
| 120 mmHg | 0.1579 atm | millimeter of mercurys to standard atmospheres |
| 200 mmHg | 0.2632 atm | millimeter of mercurys to standard atmospheres |
| 300 mmHg | 0.3947 atm | millimeter of mercurys to standard atmospheres |
| 400 mmHg | 0.5263 atm | millimeter of mercurys to standard atmospheres |
| 500 mmHg | 0.6579 atm | millimeter of mercurys to standard atmospheres |
| 600 mmHg | 0.7895 atm | millimeter of mercurys to standard atmospheres |
| 700 mmHg | 0.9211 atm | millimeter of mercurys to standard atmospheres |
| 760 mmHg | 1 atm | millimeter of mercurys to standard atmospheres |
| 1,000 mmHg | 1.3158 atm | millimeter of mercurys to standard atmospheres |
| 1,520 mmHg | 2 atm | millimeter 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 |
| millimeter 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 Institute of Standards and Technology (NIST) — United States's national measurement authority.
Last checked: September 2026. Conversion factors are fixed by definition and do not change with tax years or regulations.