Convert Standard Atmospheres to Millibars
Convert Standard Atmospheres (atm) to Millibars (mbar) instantly and accurately.
Conversion Formula
mbar = atm × 1013.25
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.
About Millibars
A millibar (mbar) = 100 Pa = 1 hPa - the historically dominant meteorological pressure unit. Standard sea-level pressure is 1013.25 mbar. Hurricane intensity is characterised by central pressure: Category 5 storms typically below 920 mbar (US record: 892 mbar, 1935). Upper-air analysis levels - 850, 700, 500, 300, 200 mbar - appear throughout decades of archived meteorological data. Aircraft cabins are pressurised to ~750-800 mbar at cruise altitude. 'Weather bombs' see pressure fall 24+ mbar in 24 hours. 1 mbar = 100 Pa.
Quick Reference Table
| Standard Atmospheres (atm) | Millibars (mbar) |
|---|---|
| 1 atm | 1013.25 mbar |
| 2 atm | 2026.5 mbar |
| 5 atm | 5066.25 mbar |
| 10 atm | 10132.5 mbar |
| 25 atm | 25331.3 mbar |
| 50 atm | 50662.5 mbar |
| 100 atm | 101325 mbar |