Convert Inches of Mercury to Standard Atmospheres
Convert Inches of Mercury (inHg) to Standard Atmospheres (atm) instantly and accurately.
Conversion Formula
atm = inHg × 0.03342105739
About Inches of Mercury
One inch of mercury (inHg) ≈ 3,386 Pa - the primary barometric pressure unit in US aviation and meteorology. ASOS weather stations, METARs, and altimeter settings in the US report in inHg. Standard sea-level pressure is 29.92 inHg. Altimeters are set to local QNH in inHg to maintain altitude reference. US barometers for home weather stations display inHg. Typical pressure range: 28.5-31.0 inHg in continental weather systems. Record low: ~25.70 inHg (Typhoon Tip, 1979). 1 inHg = 3,386.39 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
| Inches of Mercury (inHg) | Standard Atmospheres (atm) |
|---|---|
| 1 inHg | 0.0334211 atm |
| 2 inHg | 0.0668421 atm |
| 5 inHg | 0.167105 atm |
| 10 inHg | 0.334211 atm |
| 25 inHg | 0.835526 atm |
| 50 inHg | 1.67105 atm |
| 100 inHg | 3.34211 atm |