Pressure units at a glance
Every pressure unit is a fixed multiple of the pascal, the SI unit of pressure — one newton per square metre. The pascal is tiny in everyday terms, which is why practical work uses kilopascals, bars or psi instead.
| Unit | Symbol | In pascals |
|---|---|---|
| Pascal | Pa | 1 Pa |
| Hectopascal | hPa | 100 Pa |
| Kilopascal | kPa | 1,000 Pa |
| Megapascal | MPa | 1,000,000 Pa |
| Millibar | mbar | 100 Pa |
| Bar | bar | 100,000 Pa |
| Pound per square inch | psi | 6,894.757293 Pa |
| Atmosphere | atm | 101,325 Pa |
| Millimetre of mercury | mmHg | 133.322387 Pa |
| Inch of mercury | inHg | 3,386.388640 Pa |
A hectopascal and a millibar are the same size, which is why weather reports can quote 1013 hPa and 1013 mbar interchangeably.
The conversions people need most
- PSI to bar: divide by 14.5037738, or multiply by 0.0689476.
- Bar to PSI: multiply by 14.5037738.
- PSI to kPa: multiply by 6.8947573.
- Bar to kPa: multiply by 100.
- atm to bar: multiply by 1.01325.
For tyre pressures, a useful rule of thumb is that 1 bar is about 14.5 psi, so a 30 psi tyre is a little over 2 bar.
More pressure conversions
Need a conversion specifically between psi and bar? Use the dedicated PSI to Bar Converter or Bar to PSI Converter. For other pressure units, use the converter above to switch between any supported pair.
Why psi is not a round number
Metric pressure units convert between each other by powers of ten, but psi doesn't, because it's built from pounds and inches. One pound-force is 4.4482216152605 newtons and one square inch is 0.00064516 square metres, so 1 psi works out at 6,894.757293168... pascals. That's a defined value, not a measurement, but it isn't a tidy one — which is why psi conversions run on forever as decimals and this converter marks rounded results.
Gauge pressure and absolute pressure
A tyre gauge reading 32 psi means 32 psi above the surrounding air, not 32 psi in total — that's gauge pressure, sometimes written psig. Absolute pressure counts from a vacuum and would be about 46.7 psi for the same tyre at sea level. Unit conversion works the same way for both, but the two aren't interchangeable, so keep track of which one your figure is.
Frequently asked questions
How many psi are in a bar?
1 bar is 14.5037738 psi. Going the other way, 1 psi is 0.0689476 bar. For a direct conversion, see the Bar to PSI Converter or PSI to Bar Converter. Neither is a round number, because bar is metric and psi is imperial.
Is 1 bar the same as 1 atmosphere?
Close but not equal. 1 atm is 101,325 Pa and 1 bar is 100,000 Pa, so an atmosphere is about 1.3% larger. The bar is defined as exactly 100,000 Pa, while the standard atmosphere is defined as exactly 101,325 Pa.
Why do weather forecasts use hPa and mbar?
Because they're the same size — 1 hPa = 1 mbar = 100 Pa. Meteorology used millibars for decades, and when the SI switched things to pascals, hectopascals happened to match the existing numbers exactly, so no forecast values had to change.