A millibar is 100 pascals.
Millibars to Atmospheres Converter — mbar to atm
Convert Millibar (mbar) to Atmosphere (atm) using the exact conversion factor (1 millibar = 0.0009869233 atmosphere). See the formula, worked examples, conversion table, and common uses.
Millibars to Atmospheres converter
Converter
Pressure Converter
Convert pascals, bars, PSI, atmospheres, mercury columns, water columns, and engineering pressure units.
Context values
Some unit families need one extra value for a physically accurate result.
A standard atmosphere is exactly 101,325 pascals.
Result = input x 100 / 101325.
Pressure uses the pascal as the base unit.
Reserved above the conversion cards and below the converter.
About Converting Millibars to Atmospheres
Millibar and Atmosphere both show up on pressure gauges — psi is standard on US tire and tool specifications, while bar is the everyday pressure unit across most of the rest of the world. Specifically: A millibar is 100 pascals, and a standard atmosphere is exactly 101,325 pascals.
Formula
atmospheres = millibars × 0.000986923266716
This factor comes from each unit's defined relationship to the category's base unit: 1 millibar equals 100 base units, and 1 atmosphere equals 101325 base units, so dividing one by the other gives the direct millibar-to-atmosphere factor of 0.000986923266716.
Simple example
1 mbar × 0.0009869232667 = 0.0009869233 atm
1 millibar = 0.0009869233 atmospheres.
Real-world example
35 mbar × 0.0009869232667 = 0.0345423143 atm
35 millibars = 0.0345423143 atmospheres.
Conversion table
| Millibar (mbar) | Atmosphere (atm) |
|---|---|
| 1 mbar | 0.0009869233 atm |
| 5 mbar | 0.0049346163 atm |
| 10 mbar | 0.0098692327 atm |
| 25 mbar | 0.0246730817 atm |
| 50 mbar | 0.0493461633 atm |
| 100 mbar | 0.0986923267 atm |
Reverse conversion: Atmosphere to Millibar
0.0009869233 atm × 1013.25 = 1.000000034 mbar
0.0009869233 atmospheres = 1.000000034 millibars.
millibars = atmospheres × 1013.25
For a page dedicated to this direction, see Atmosphere to Millibar.
Understanding the Millibar (mbar)
A millibar is 100 pascals.
Understanding the Atmosphere
Atmosphere (atm) measures pressure. Defined as exactly 101,325 pascals, originally based on the average atmospheric pressure at mean sea level. It is classified as a non-SI unit accepted for use with the SI.
Where it's used: Widely used internationally in chemistry, meteorology, and diving/aviation contexts alongside the pascal and bar
Uses of the Atmosphere today
- Chemistry (standard conditions are often defined at 1 atm)
- Diving and aviation pressure references
- General reference for everyday atmospheric pressure
Atmosphere — sources
- BIPM SI Brochure — Standard atmosphere listed among non-SI units with a fixed exact value in pascals.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many atmospheres are in 1 millibar?
1 millibar equals 0.0009869233 atmospheres, using the exact defined conversion factor rather than an estimate.
How do I convert millibar to atmosphere?
Multiply the millibar value by 0.0009869232667. The converter above does this instantly to whatever precision you set.
How do I convert atmosphere back to millibar?
Use the reverse factor: 1 atmosphere equals 1,013.25 millibars. You can also use the swap control in the converter above to flip the direction instantly.
What is a millibar?
Millibar (mbar) is a unit of pressure.
What is a atmosphere?
Atmosphere (atm) measures pressure. Defined as exactly 101,325 pascals, originally based on the average atmospheric pressure at mean sea level. It is classified as a non-SI unit accepted for use with the SI.
Is the millibar to atmosphere conversion exact?
Yes. Defined as exactly 101,325 pascals, originally based on the average atmospheric pressure at mean sea level. That fixed definition is what the converter above uses, so any rounding you see is a display choice, not a limitation of the math.