A standard atmosphere is exactly 101,325 pascals.
Atmospheres to Bars Converter — atm to bar
Convert Atmosphere (atm) to Bar (bar) using the exact conversion factor (1 atmosphere = 1.01325 bar). See the formula, worked examples, conversion table, unit comparison, history, and common uses.
Atmospheres to Bars 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 bar is exactly 100,000 pascals.
Result = input x 101325 / 100000.
Pressure uses the pascal as the base unit.
Reserved above the conversion cards and below the converter.
About Converting Atmospheres to Bars
Atmosphere and Bar 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. Atmosphere is typically associated with widely used internationally in chemistry, meteorology, and diving/aviation contexts alongside the pascal and bar, while Bar is typically associated with widely used in Europe and most of the world for tire pressure, weather, and industrial pressure.
Formula
bars = atmospheres × 1.01325
This factor comes from each unit's defined relationship to the category's base unit: 1 atmosphere equals 101325 base units, and 1 bar equals 100000 base units, so dividing one by the other gives the direct atmosphere-to-bar factor of 1.01325.
Simple example
1 atm × 1.01325 = 1.01325 bar
1 atmosphere = 1.01325 bars.
Real-world example
35 atm × 1.01325 = 35.46375 bar
35 atmospheres = 35.46375 bars.
Conversion table
| Atmosphere (atm) | Bar (bar) |
|---|---|
| 1 atm | 1.01325 bar |
| 5 atm | 5.06625 bar |
| 10 atm | 10.1325 bar |
| 25 atm | 25.33125 bar |
| 50 atm | 50.6625 bar |
| 100 atm | 101.325 bar |
Reverse conversion: Bar to Atmosphere
1.01325 bar × 0.9869232667 = 1 atm
1.01325 bars = 1 atmosphere.
atmospheres = bars × 0.986923266716
For a page dedicated to this direction, see Bar to Atmosphere.
Atmosphere vs. Bar
| Aspect | Atmosphere | Bar |
|---|---|---|
| Family | non-SI unit accepted for use with the SI | Non-SI metric unit accepted for use with SI |
| Typical use | Chemistry (standard conditions are often defined at 1 atm) | Tire pressure specifications outside the US |
| Where it's used | Widely used internationally in chemistry, meteorology, and diving/aviation contexts alongside the pascal and bar | Widely used in Europe and most of the world for tire pressure, weather, and industrial pressure |
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
Understanding the Bar
Bar (bar) measures pressure. A bar is defined as exactly 100,000 pascals, close to (but distinct from) one standard atmosphere (101,325 Pa). It is classified as a Non-SI metric unit accepted for use with SI.
Where it's used: Widely used in Europe and most of the world for tire pressure, weather, and industrial pressure
Uses of the Bar today
- Tire pressure specifications outside the US
- Meteorology (weather maps commonly use millibars, hPa)
- Industrial and hydraulic pressure ratings in metric-system countries
History of the Bar
The bar was proposed by Norwegian meteorologist Vilhelm Bjerknes around 1906 as a convenient round pressure unit close to atmospheric pressure, derived from the CGS unit system (one bar equals one million dynes per square centimeter).
Though not an SI unit, the bar remains in wide practical use, particularly in meteorology (as the millibar, now more often written as the equivalent hectopascal) and in tire and hydraulic pressure specifications across most of the world.
Historical origin. Bar was not the invention of a single named person; it developed through the process described above.
Atmosphere — sources
- BIPM SI Brochure — Standard atmosphere listed among non-SI units with a fixed exact value in pascals.
Bar — sources
- BIPM SI Brochure — Non-SI units accepted for use with SI — Lists the bar among accepted non-SI pressure units.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many bars are in 1 atmosphere?
1 atmosphere equals 1.01325 bars, using the exact defined conversion factor rather than an estimate.
How do I convert atmosphere to bar?
Multiply the atmosphere value by 1.01325. The converter above does this instantly to whatever precision you set.
How do I convert bar back to atmosphere?
Use the reverse factor: 1 bar equals 0.9869232667 atmospheres. You can also use the swap control in the converter above to flip the direction instantly.
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.
What is a bar?
Bar (bar) measures pressure. A bar is defined as exactly 100,000 pascals, close to (but distinct from) one standard atmosphere (101,325 Pa). It is classified as a Non-SI metric unit accepted for use with SI.
Is the atmosphere to bar conversion exact?
Yes. A bar is defined as exactly 100,000 pascals, close to (but distinct from) one standard atmosphere (101,325 Pa). That fixed definition is what the converter above uses, so any rounding you see is a display choice, not a limitation of the math.
Where is the atmosphere still used today?
Widely used internationally in chemistry, meteorology, and diving/aviation contexts alongside the pascal and bar