Atmospheres to Millibars
One atmosphere is the average air pressure at sea level, used as a reference unit in chemistry and physics. A millibar is one thousandth of a bar, the standard unit meteorologists use for barometric pressure readings. 1 atm equals 1,013.25 mbar, so converting between them is a matter of multiplying by that fixed factor — type any value into the converter below and both sides update instantly as you type.
Both units belong to pressure, measured here against pressure's base unit (Pa) — every other pressure unit on this site converts through that same reference point, which is why the table below can also be read as a quick cross-check against nearby values.
Formula
mbar = atm × 1,013.25
atm = mbar × ≈0.000986923
Worked example: 5 atm × 1,013.25 = 5,066.25 mbar.
Conversion table
| Atmosphere (atm) | Millibar (mbar) |
|---|---|
| 1 atm | 1,013.25 mbar |
| 2 atm | 2,026.5 mbar |
| 3 atm | 3,039.75 mbar |
| 5 atm | 5,066.25 mbar |
| 10 atm | 10,132.5 mbar |
| 20 atm | 20,265 mbar |
| 25 atm | ≈25,331.3 mbar |
| 50 atm | 50,662.5 mbar |
| 100 atm | 101,325 mbar |
| 250 atm | ≈253,313 mbar |
| 500 atm | 506,625 mbar |
| 1,000 atm | 1,013,250 mbar |
Frequently asked
- How many Millibars in a atmosphere?
- 1 atm equals 1,013.25 mbar.
- How do I convert Atmospheres to Millibars?
- Multiply the value in atm by 1,013.25 to get mbar. The converter above does this instantly as you type.
- Is the conversion exact?
- Yes — Atmosphere and Millibar are both defined by a fixed conversion factor to pressure's base unit (Pa), so the result shown is exact to the precision displayed, not an approximation.