Convert Millimeters of Mercury to Standard Atmospheres
Convert Millimeters of Mercury (mmHg) to Standard Atmospheres (atm) instantly and accurately.
Conversion Formula
atm = mmHg × 0.001315789661
About Millimeters of Mercury
One millimetre of mercury (mmHg) = pressure from 1 mm of mercury at 0°C and standard gravity = 133.322 Pa. Clinical medicine worldwide uses mmHg for blood pressure (normal ~120/80 mmHg) and for gas partial pressures in physiology: arterial O₂ ~95-100 mmHg; CO₂ ~40 mmHg; alveolar O₂ ~104 mmHg. Ophthalmologists measure intraocular pressure in mmHg (normal 10-21; glaucoma risk above 21). Vacuum equipment ratings are also given in mmHg. 760 mmHg = 1 atm. 1 mmHg = 133.322 Pa.
About Standard Atmospheres
The standard atmosphere (atm) = exactly 101,325 Pa - defined by the 10th CGPM (1954) as the reference air pressure at sea level. Used to define STP (0°C and 1 atm) for gas law and thermochemistry. Chemical equilibrium constants (Kp), Henry's law solubility, and thermodynamic tables are tabulated at 1 atm. ISA aviation standard: sea-level 1 atm / 15°C, pressure halving every ~5.5 km. Diving physics: +1 atm per 10 m depth (fresh water) so 30 m = 4 atm absolute. Diamond formation in Earth's mantle: ~50,000 atm. 1 atm = 101,325 Pa.
Quick Reference Table
| Millimeters of Mercury (mmHg) | Standard Atmospheres (atm) |
|---|---|
| 1 mmHg | 0.00131579 atm |
| 2 mmHg | 0.00263158 atm |
| 5 mmHg | 0.00657895 atm |
| 10 mmHg | 0.0131579 atm |
| 25 mmHg | 0.0328947 atm |
| 50 mmHg | 0.0657895 atm |
| 100 mmHg | 0.131579 atm |