Is 1 bar equal to 1 atmosphere?

Nearly, but not exactly. 1 bar = 0.9869 atm; 1 atm = 1.0133 bar.

Why is standard pressure sometimes quoted as 1 bar instead of 1 atm?

In 1982 IUPAC adopted 100 kPa (1 bar) as the standard for thermodynamic tables, replacing 101.325 kPa (1 atm). Both are used in different contexts.

Bar to Atmospheres Converter

Convert bar to atmospheres for chemistry, diving tables, and gas pressure comparisons. The bar is close to, but slightly less than, one standard atmosphere.

Formula

Divide bar by 1.01325 to get atmospheres. To reverse, multiply atmospheres by 1.01325 to get bar.

Quick reference

Bar (bar)	Atmosphere (atm)
0.5	0.4934616
1	0.9869233
1.5	1.480385
2	1.973847
3	2.96077
5	4.934616
10	9.869233
20	19.73847
50	49.34616
100	98.69233

About these units

Bar

The bar (100,000 Pa) was defined in 1909 by the Norwegian meteorologist Vilhelm Bjerknes. Its near-equivalence to one atmosphere made it convenient for meteorology and oceanography.

Atmosphere

The standard atmosphere (101,325 Pa) was fixed in 1954. The near-identity of bar and atm means that 1 bar ≈ 0.987 atm, making conversions between them simple approximations.

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