How to Convert Millibars to Atmospheres (mbar to atm)
Pressure conversions are used for tyre pressure (psi or bar), blood pressure readings in mmHg and weather maps in millibars. This guide shows how to convert millibars into atmospheres by hand, with examples and a quick-reference table.
The conversion
To convert millibars to atmospheres, multiply the value by 0.0009869233. To go the other way, divide by the same number (or multiply by 1,013.25). Because the factor is tiny, scientific notation keeps the numbers manageable.
Atmospheres = millibars × 0.0009869233
Worked examples
- 3 mbar = 0.002961 atm
- 12.5 mbar = 0.012337 atm
- 75 mbar = 0.074019 atm
Millibars to Atmospheres table
| Millibars | Atmospheres |
|---|---|
| 1 mbar | 0.000987 atm |
| 2 mbar | 0.001974 atm |
| 5 mbar | 0.004935 atm |
| 10 mbar | 0.009869 atm |
| 20 mbar | 0.019738 atm |
| 25 mbar | 0.024673 atm |
| 50 mbar | 0.049346 atm |
| 100 mbar | 0.098692 atm |
| 250 mbar | 0.246731 atm |
| 500 mbar | 0.493462 atm |
| 1,000 mbar | 0.986923 atm |
Common questions
Is mbar to atm exact?
The factors used here are the internationally defined values where they exist; results are rounded for display only.
How do I convert back?
Use the Atmospheres to Millibars converter.
Mistakes to avoid
Multiplying when you should divide
Converting to a smaller unit gives a bigger number, and converting to a larger unit gives a smaller one. If your answer moves the wrong way, you have inverted the factor.
Mixing similar-sounding units
US and imperial gallons, pints and tons are different sizes, and decimal kilobytes differ from binary kibibytes.
Rounding the factor too early
Using 3 instead of 3.28 for feet per metre introduces an error of almost 9% before you have started.
Background
A conversion table is handy for common values, but a calculator is faster and avoids interpolation errors for anything in between.
Unit conversion is simply multiplication by a fixed ratio. The ratio between two units of the same quantity never changes, so once you know it you can convert any value in either direction.
For everyday use, three or four significant figures are usually enough. Engineering, science and trade documents may need more, and rounding should happen only at the end of a calculation.
For any value, use the Millibars to Atmospheres Converter or browse all pressure converters.
Run your own numbers: Millibars to Atmospheres Converter