Bar to atm Converter
A bar is defined as exactly 100,000 pascals and the standard atmosphere is defined as exactly 101,325 pascals, so bar to atm is a multiplication by 100,000/101,325, a fraction that reduces to exactly 4,000/4,053 and prints here as 0.986923266716. One bar is therefore a little under one atmosphere: 1 bar is 0.986923266716 atm, 2 bar is 1.97384653343 atm, 10 bar is 9.86923266716 atm and a 200 bar cylinder is 197.384653343 atm. The reverse direction is the tidy one, because 1 atm is exactly 1.01325 bar, so 1,013.25 bar comes back as exactly 1,000 atm. This page opens the converter with Bar in the From box and Atmosphere in the To box, ahead of whatever pair you last used, and it answers as you type, to twelve significant digits. Under the answer the same pressure is listed in pascals, kilopascals and pounds per square inch at once, so 1 bar reads 100,000 Pa, 100 kPa and 14.503773773 psi, with millimetres of mercury at 750.061575846 once the Show 1 more switch is on. It converts units and nothing else: whether the reading on your gauge is absolute or measured against the air around it is something the number alone cannot say.
1 bar in every pressure unit
Common questions
- How many atm is 1 bar?
- 0.986923266716 atm, which is about 1.3 percent short of a full atmosphere. The bar is fixed at 100,000 pascals and the standard atmosphere at 101,325 pascals, so every bar is 1,325 Pa light. The figures scale straight from there: 2 bar is 1.97384653343 atm, 3 bar is 2.96076980015 atm, 5 bar is 4.93461633358 atm, 10 bar is 9.86923266716 atm and 100 bar is 98.6923266716 atm.
- What is the formula for bar to atm?
- atm = bar × 100,000 / 101,325, which is exactly 4,000/4,053 and never terminates as a decimal, so the page rounds at twelve significant digits and shows 0.986923266716 for one bar. Going the other way is exact: bar = atm × 1.01325, so 1 atm is 1.01325 bar, 2 atm is 2.0265 bar and 10 atm is 10.1325 bar. The swap button between the two boxes turns the page around, and it keeps the number you typed rather than the answer, so it converts that same figure in the new direction.
- Why is a bar not exactly one atmosphere?
- Because the two were fixed by different conventions and neither moved afterwards. The standard atmosphere was set at 101,325 pascals, the pressure of 760 millimetres of mercury used as the sea-level reference, and the bar was set at a round 100,000 pascals to keep metric arithmetic easy. The gap is 1,325 Pa, which this page shows as 1 bar = 0.986923266716 atm and 1 atm = 1.01325 bar.
- Worked example: what is 200 bar in atmospheres?
- 197.384653343 atm. Type 200 into the From box, with or without the comma, and the answer appears as you type with no button to press. The list underneath gives the same pressure as 20,000,000 Pa, 20,000 kPa and 2,900.7547546 psi, each row with its own Copy button, while Copy result above copies the headline atm figure without the thousands separators it is displayed with.
- Is this gauge pressure or absolute pressure?
- The converter changes units and leaves that distinction exactly where it found it: a gauge reading of 1 bar becomes 0.986923266716 atm gauge, and an absolute reading of 1 bar becomes 0.986923266716 atm absolute. Moving between gauge and absolute means adding or subtracting the surrounding air pressure yourself, close to 1 atm at sea level, and nothing in a bare number tells the page which of the two you typed.
- Can it convert millibar or hectopascal?
- Not as their own entries: the pressure menu holds pascal, kilopascal, bar, pound per square inch, atmosphere and millimetre of mercury. A millibar is one thousandth of a bar, and a hectopascal is the same size, so divide the millibar figure by 1,000 and type it in the bar box. A sea-level 1,013.25 mbar is 1.01325 bar, which reads exactly 1 atm, and 1 mbar is 0.001 bar, which reads 0.000986923266716 atm.
- What is 1 bar in psi and kPa?
- 14.503773773 psi and exactly 100 kPa, both printed in the list under the answer without changing a setting, alongside 100,000 Pa. Millimetres of mercury sit behind the Uncommon units switch in the row under the converter, labelled Show 1 more on this category, where 1 bar is 750.061575846 mmHg. Picking any of those units in the To menu promotes it to the headline instead.
- How precise are the answers?
- Twelve significant digits, computed in double-precision arithmetic, which is more than a ratio defined exactly as 4,000/4,053 needs. Anything smaller than 0.000001 switches to exponential notation rather than a row of leading zeros, so 0.000001 bar reads 9.869233e-7 atm, while 0.001 bar stays decimal at 0.000986923266716 atm.
- Does anything I type leave the page?
- No. The conversion is arithmetic against a table of exact factors that ships with the page, so it runs in your browser with nothing uploaded and no account, and it keeps working with no network connection once the page has loaded.
Conversion factors are the exact legal definitions where one exists. An inch is exactly 2.54 cm and a pound exactly 0.45359237 kg, so those conversions are exact rather than approximate. Temperature uses offsets rather than factors, and that is shown in the working.