Bar to ATM Conversion Calculator — Bar to Standard Atmospheres
Convert any pressure in bar to standard atmospheres (atm) and other common units. 1 bar = 0.986923 atm — just under one atmosphere because the bar is exactly 100,000 Pa while 1 atm is 101,325 Pa.
bar
1 bar = 0.986923 atm exactly (1 atm = 101,325 Pa; 1 bar = 100,000 Pa)
- 1
Bar to pascals
1 × 100,000 = 100,000 - 2
Pascals to atm
100,000 ÷ 101,325 = 0.9869231 standard atmosphere = 101,325 Pa (exact by definition).
How does this calculator work?
1 bar = 0.986923 atm = 100 kPa = 100,000 Pa = 1,000 mbar = 750.062 mmHg = 14.5038 psi. The bar is exactly 100,000 Pa while 1 atm is 101,325 Pa — so 1 bar is about 1.3% less than one atmosphere. Divide atm by 1.01325 to get bar; multiply bar by 1.01325 to get atm.
Formula
How this is calculated
The bar and the standard atmosphere (atm) are both widely used as everyday pressure references, but they differ slightly. The bar is defined as exactly 100,000 Pa (100 kPa), a round number chosen for convenience. The standard atmosphere is defined as exactly 101,325 Pa — the mean atmospheric pressure at sea level used in the International Standard Atmosphere. Because 1 atm > 1 bar, one bar is slightly less than one atmosphere: 1 bar = 100,000 / 101,325 ≈ 0.986923 atm.
The conversion is exact (within the precision of the definitions) and involves no approximation: atm = bar × 100,000 / 101,325. Going the other direction: bar = atm × 101,325 / 100,000 = atm × 1.01325.
In practice, 1 bar is close enough to 1 atm that the two are sometimes used interchangeably in informal contexts — weather maps, for instance, label isobars in mbar (millibars) or hPa, and "one bar" is the standard state pressure in thermodynamics (replacing the older 1 atm standard). For precision work, always distinguish between the two: at sea level, measured atmospheric pressure varies from about 0.970 to 1.050 atm with weather, but the standard atmosphere is a fixed constant.
Frequently asked questions
1 bar = 100,000 Pa / 101,325 Pa per atm ≈ 0.986923 atm. In other words, one bar is about 1.3% less than one standard atmosphere.
No. 1 atm = 101,325 Pa while 1 bar = 100,000 Pa, so 1 bar ≈ 0.9869 atm. They are close but not equal. Thermodynamic standard state has used 1 bar since 1982 (IUPAC), replacing the older 1 atm standard.
Use bar when quoting industrial pressures, gas cylinder contents, or working with SI-adjacent fields (meteorology uses mbar/hPa; chemistry uses bar for standard state). Use atm when referencing the International Standard Atmosphere, scuba depth calculations, or comparing to older thermodynamic tables that used the 1 atm convention.
TG we-Calculate Editorial Team. (2026). Bar to ATM Conversion Calculator — Bar to Standard Atmospheres [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/bar-to-atm-conversion-calculator
TG we-Calculate Editorial Team. "Bar to ATM Conversion Calculator — Bar to Standard Atmospheres." TG we-Calculate. 2026. https://we-calculate.com/calculator/bar-to-atm-conversion-calculator.
TG we-Calculate Editorial Team, "Bar to ATM Conversion Calculator — Bar to Standard Atmospheres," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/bar-to-atm-conversion-calculator
@misc{wecalculate_bar_to_atm_conversion_calculator, title = {Bar to ATM Conversion Calculator — Bar to Standard Atmospheres}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/bar-to-atm-conversion-calculator}}, year = {2026}, note = {TG we-Calculate} }
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