Atmospheres to Bar
Enter atmospheres and read bar. One standard atmosphere is exactly 101,325 Pa, and one bar is 100,000 Pa, so 1 atm = 1.01325 bar.
Formula: bar = atm × 1.01325
- Standard atmosphere (atm)
- Also called atmosphere · standard pressure
- A fixed pressure of exactly 101,325 pascals, adopted in 1954 as a reference for average air pressure at sea level. It is a defined value, not a measurement of today's weather.
Atm to bar table
| Standard atmospheres (atm) | Bar (bar) |
|---|---|
| 1 | 1.01325 |
| 2 | 2.0265 |
| 3 | 3.03975 |
| 4 | 4.053 |
| 5 | 5.06625 |
| 6 | 6.0795 |
| 7 | 7.09275 |
| 8 | 8.106 |
| 9 | 9.11925 |
| 10 | 10.1325 |
| Standard atmospheres (atm) | Bar (bar) |
|---|---|
| 12 | 12.159 |
| 15 | 15.19875 |
| 20 | 20.265 |
| 25 | 25.33125 |
| 30 | 30.3975 |
| 40 | 40.53 |
| 50 | 50.6625 |
| 60 | 60.795 |
| 75 | 75.99375 |
| 100 | 101.325 |
Where the two units show up
Chemistry and physics textbooks, gas laws and older engineering tables use the atmosphere because it describes pressure relative to the air around us. Industry, diving and European equipment labels use the bar, which is a round 100 kPa. A pressure cooker rated at 2 atm absolute works at about 2.03 bar; a gas cylinder test at 10 atm is about 10.13 bar.
Weather maps use hectopascals, which are the same size as millibars. Standard sea-level pressure is 1013.25 hPa, which is 1 atm and 1.01325 bar written another way.
Gas suppliers, compressor makers and lab glassware rated for pressure may use any of the three units, atm, bar or kPa, sometimes on the same label. Converting to one unit before you compare two ratings avoids reading a 1.3% gap as a safety margin, or missing one that is real.
Two definitions, no measurement
Neither unit depends on a measurement of the air. The atmosphere was set by the CGPM as exactly 101,325 Pa, and the bar is defined as 10⁵ Pa. That makes the ratio between them exact, with nothing to round except the result you choose to display. NIST lists both in Special Publication 811.
For tire and equipment pressures in US units, bar to psi and psi to bar handle the step, and kPa to psi covers metric gauges in kilopascals.
One atmosphere in other pressure units
One standard atmosphere in every other pressure unit on this site
- Kilopascals101.325 kPa
- Bar1.01325 bar
- Pounds per square inch14.695949 psi
Atm to bar questions
What is one standard atmosphere in bar?
Exactly 1.01325 bar. The two units are close enough that rough work often treats them as equal, but the difference is 1.3%.
Is atmospheric pressure always 1 atm?
No. The standard atmosphere is a reference value. Real air pressure at sea level changes with the weather, usually between about 0.97 and 1.04 atm, and drops with altitude.
What is 3 atm in bar?
3.03975 bar.
Why do divers say every 10 m adds one atmosphere?
Ten meters of seawater press down with roughly one more atmosphere of pressure. At 30 m a diver is under about 4 atm absolute: one from the air plus three from the water.