Bar to ATM Pressure Converter
Enter a pressure in bar to convert it to standard atmospheres (atm) and six other common units simultaneously. Switch the input unit to go the other direction: atm, kPa, Pa, psi, torr, or mbar all convert back to bar and to each other. The conversion factor, a step-by-step breakdown, and a reference table of real-world pressures are included below.
Formula
Worked example
Convert 3 bar to atm: 3 ÷ 1.01325 = 2.96077 atm. Reverse: 2.96077 × 1.01325 = 3 bar.
Bar and atm: what they measure
Pressure is the force per unit area exerted by a fluid on a surface. Two of the most common units for moderate pressures are the bar and the standard atmosphere (atm). The bar was adopted by the International Union of Pure and Applied Chemistry (IUPAC) in 1982 as the standard reference pressure, defined as exactly 100,000 pascals. The standard atmosphere, by contrast, is defined as exactly 101,325 pascals, the approximate pressure of the Earth's atmosphere at sea level and 0 degrees Celsius. Because they are so close in magnitude, bar and atm are often used interchangeably, but they differ by about 1.3% and that gap matters in precise scientific work.
The conversion formula
Because both units are fixed multiples of the pascal, converting between them is a single multiplication or division. To convert bar to atm, divide by 1.01325 (the ratio of atm to bar). To convert atm to bar, multiply by 1.01325. The reciprocal factor is 0.986923, so 1 bar equals 0.986923 atm exactly. In practice: 1 bar = 0.986923 atm, 1 atm = 1.01325 bar. No temperature or pressure corrections are needed because these are unit definitions, not physical measurements.
Other pressure units in this converter
This calculator also outputs kilopascals (kPa), pascals (Pa), pounds per square inch (psi), torr, and millibar (mbar). A kilopascal is 1,000 pascals and equals 0.01 bar. A pascal is the SI base unit, 1 newton per square metre. PSI is the imperial unit used in the USA for tire pressures and industrial gauges. Torr (and its equivalent mmHg, millimetres of mercury) is used in medicine and vacuum engineering. Millibar is the unit of choice in meteorology: standard sea-level pressure is 1,013.25 mbar.
Real-world pressure contexts
Standard sea-level atmospheric pressure is 1.01325 bar (1 atm). A bicycle tire runs at roughly 6 to 9 bar, a car tire at about 2 to 2.5 bar, and an espresso machine at 9 bar. Scuba cylinders are charged to 200 to 300 bar. Vacuum systems used in semiconductor manufacture may reach pressures below 0.001 mbar. Weather systems in meteorology are tracked in mbar: a strong hurricane eye may drop below 920 mbar, while a high-pressure ridge can exceed 1,040 mbar (about 1.04 bar). Knowing which unit fits a given context makes converting between them easier to sanity-check.
Common pressures in bar and atm
| Context | bar | atm | kPa | psi |
|---|---|---|---|---|
| Perfect vacuum | 0 | 0 | 0 | 0 |
| Mars surface (average) | 0.006 | 0.006 | 0.6 | 0.09 |
| Lung pressure (exhale) | 0.10 | 0.099 | 10 | 1.45 |
| Standard atmosphere (sea level) | 1.01325 | 1.000 | 101.3 | 14.70 |
| Standard bar (IUPAC reference) | 1.000 | 0.987 | 100.0 | 14.50 |
| Car tire (typical gauge) | 2.2 | 2.17 | 220 | 31.9 |
| Espresso machine | 9 | 8.88 | 900 | 130.5 |
| Scuba tank (full) | 200 | 197 | 20,000 | 2,901 |
| Deep-sea (1,000 m depth) | 101 | 99.7 | 10,100 | 1,465 |
Reference values for everyday and scientific pressure contexts.
Frequently asked questions
What is 1 bar in atm?
1 bar equals 0.986923 standard atmospheres. The conversion comes from the definitions: 1 bar = 100,000 Pa and 1 atm = 101,325 Pa, so 1 bar = 100,000 / 101,325 = 0.986923 atm.
What is 1 atm in bar?
1 standard atmosphere equals 1.01325 bar exactly. This is a definition: the standard atmosphere was historically set as the average sea-level air pressure, which is slightly above 1 bar.
Is bar the same as atm?
They are close but not equal. 1 bar = 0.986923 atm (a difference of about 1.3%). In everyday contexts such as tire pressures and weather reports, the difference is negligible, but in precise scientific calculations such as gas law problems or thermodynamic tables, use the exact factor.
Why do some sources say 1 bar is approximately 1 atm?
Because the two units differ by only 1.3%, many engineers and scientists treat them as interchangeable for rough estimates. The IUPAC switched its standard reference pressure from 1 atm to 1 bar in 1982 precisely because 100,000 Pa (1 bar) is a rounder number than 101,325 Pa (1 atm). Tabulated gas properties published before 1982 may reference 1 atm rather than 1 bar.
How do I convert bar to kPa?
1 bar = 100 kPa exactly. Multiply the bar value by 100 to get kilopascals, or divide kilopascals by 100 to get bar. For example, 2.5 bar = 250 kPa.
How do I convert bar to psi?
1 bar = 14.5038 psi (pounds per square inch). Multiply bar by 14.5038 to get psi. For example, 2 bar = 29.008 psi. This converter shows psi automatically in the output table.
What pressure unit should I use for tire pressure?
Car tire pressures in Europe and much of Asia are quoted in bar; in the United States they are typically quoted in psi. Standard car tires run at 2.0 to 2.5 bar (29 to 36 psi). Both units appear in the output table so you can read the right value for your region.