Bar to Atmospheres
Convert bar to atmosphere instantly — type a value and read the result, with the exact formula shown.
Example
1 bar = 0.9869233 atm, 5 bar = 4.934616 atm, 10 bar = 9.869233 atm.
How it works
Atmosphere = Bar × 0.9869233. Every value is converted through a single pascal base unit using internationally defined conversion factors, so any from/to pair stays consistent.
Good to know
Converting bar to standard atmospheres (atm) comes up most often when you bridge two different worlds of pressure measurement: the bar dominates European meteorology, scuba diving, and industrial equipment datasheets, while the atmosphere is the classic reference unit for chemistry, gas laws, and altitude or vacuum work. If you read a tyre pressure, a dive computer, or a weather chart in bar but need to plug the figure into a chemistry equation or compare it against "1 atmosphere" of normal air pressure, this is the conversion you reach for.
The two units have very different origins. The bar is a metric-adjacent unit defined cleanly as exactly 100,000 pascals, introduced in the 1900s by meteorologist Vilhelm Bjerknes so that average sea-level pressure would land near a round number. The standard atmosphere, by contrast, is a physical reference: it was fixed by definition as 101,325 pascals, the agreed value of typical air pressure at sea level. Because both are anchored to the pascal, the conversion factor is exact rather than empirical.
The rule of thumb worth memorising is that a bar and an atmosphere are almost the same thing — they differ by only about 1.3%. One bar is 0.9869 atm (a touch less than one atm), and one atm is 1.01325 bar (a touch more than one bar). For quick mental math you can treat them as roughly equal and then nudge: multiply bar by 0.987 to get atm, or just subtract about 1.3% for a near-instant estimate.
- The most common mistake is assuming bar and atm are identical — they are close but not equal, so the small gap matters in precise lab work, high-pressure cylinders, or anything multiplied over many bars.
- Watch the direction: 1 bar = 0.9869233 atm but 1 atm = 1.01325 bar, and the two factors are reciprocals, not the same number — mixing them up flips your error in the wrong direction.
Frequently asked questions
How do you convert bar to atmosphere?
Multiply the number of bars by 0.9869233 to get atmospheres. For example, 1 bar = 0.9869233 atm.
What is 1 bar in atmospheres?
1 bar equals 0.9869233 atmospheres (1 bar = 0.9869233 atm).
How many bars are in 1 atmosphere?
There are 1.01325 bars in 1 atmosphere.
Is this converter free and private?
Yes. It runs entirely in your browser, so your inputs never leave your device, there is no sign-up, and it works offline once loaded.
Are the conversions exact?
Conversions use internationally defined factors and are exact where the definitions are exact (for example, 1 inch = 2.54 cm). Displayed results are rounded for readability.
People also ask
Is 1 bar the same as 1 atmosphere?
No, but they are very close. 1 bar equals 0.9869233 atm, which is about 1.3% less than one standard atmosphere; conversely 1 atm equals 1.01325 bar.
How do I convert 2 bar to atm?
Multiply by 0.9869233, so 2 bar = 1.9738466 atm, or roughly 1.97 atm.
What is the exact conversion factor from bar to atm?
1 bar = 0.9869233 atm. This comes from the exact definitions: 1 bar = 100,000 Pa and 1 standard atmosphere = 101,325 Pa, so 100000 / 101325 = 0.9869233.
How many atmospheres is 10 bar?
10 bar equals 9.869233 atm. Each bar is just under one atmosphere, so 10 bar lands a bit short of 10 atm.
Why is an atmosphere slightly more than a bar?
Because the standard atmosphere was fixed at 101,325 pascals to match typical sea-level air pressure, while the bar was defined as a round 100,000 pascals. The atmosphere is therefore 1,325 Pa (about 1.3%) larger.
Should I use bar or atm for scuba diving pressure?
Diving and most European gauges use bar, where every 10 metres of seawater adds about 1 bar. Since 1 bar is 0.9869 atm, divers often treat bar and atmospheres as practically interchangeable for depth estimates.
How do I convert atm back to bar?
Multiply atmospheres by 1.01325. For example, 3 atm = 3.03975 bar. This is the reciprocal of the bar-to-atm factor of 0.9869233.
Is the bar-to-atm conversion exact?
Yes. Both units are defined exactly in pascals (100,000 Pa and 101,325 Pa), so the ratio 0.9869233 is exact, though displayed results are usually rounded for readability.
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