Where each pressure unit is used
- Pascal (Pa) is the SI unit. Kilopascals (kPa) appear on tire placards in many countries.
- Bar is 100 kPa, close to the air pressure at sea level. Used for tires, bikes, diving and espresso machines in Europe.
- psi (pounds per square inch) is used for tires and tools in the US.
- Hectopascal (hPa) equals the millibar (mbar) and is the standard unit for air pressure in weather reports. Normal air pressure is 1013.25 hPa.
- mmHg and inHg come from mercury barometers. Blood pressure is measured in mmHg, and US weather and aviation use inHg.
- Atmosphere (atm) is the standard air pressure at sea level, 101,325 Pa.
Tire and tank gauges show gauge pressure, the pressure above the surrounding air. Absolute pressure adds about 1 bar (14.7 psi). Convert gauge to gauge and absolute to absolute.
Common pressure conversions
| From | Equals |
|---|---|
| 1 bar | 14.50377377 pounds per square inch |
| 1 pound per square inch | 0.06894757293 bar |
| 1 pound per square inch | 6.894757293 kilopascals |
| 1 atmosphere | 1,013.25 hectopascals |
| 1 atmosphere | 14.69594878 pounds per square inch |
| 1 millimeter of mercury | 0.1333223684 kilopascals |
| 1 inch of mercury | 33.86388158 hectopascals |
Tire pressure: psi to bar
| Pounds per square inch (psi) | Bar (bar) |
|---|---|
| 26 | 1.79 |
| 28 | 1.93 |
| 30 | 2.07 |
| 32 | 2.21 |
| 33 | 2.28 |
| 34 | 2.34 |
| 35 | 2.41 |
| 36 | 2.48 |
| 38 | 2.62 |
| 40 | 2.76 |
| 44 | 3.03 |
| 50 | 3.45 |
| 60 | 4.14 |
Where the conversions come up
Tires are the everyday case. The sticker in your door frame might say 2.3 bar or 230 kPa, the gauge at the petrol station reads psi, and a bike pump has both scales in tiny print. Scuba divers convert bar and psi between European and American gear, baristas talk about 9 bar of espresso pressure, and anyone following a forecast on both sides of the Atlantic meets inHg on one side and hPa on the other. Blood pressure stays in mmHg almost everywhere.
Shortcuts: bar to psi is times 14.5, psi to bar is divide by 14.5. One bar is close to one atmosphere and to 1,000 hPa. For tires, 30 psi is about 2.1 bar and 35 psi about 2.4 bar.
How to use it
- 1Choose the unit from the sticker or gauge on the left and the unit on your pump or instrument on the right.
- 2Type the reading. Typing on the right converts the other way, and swap exchanges the units.
- 3Read the result, then check the list below for the same pressure in kPa, atm, mmHg and the rest. Copy the number or a link.
Frequently asked questions
How many psi is 2.5 bar?
About 36.3 psi. One bar is about 14.5 psi, so multiply bar by 14.5 for a quick estimate.
Is a bar the same as an atmosphere?
Almost. One atmosphere is 1.01325 bar, so the two differ by about 1.3 percent.
Are hPa and mbar the same?
Yes. One hectopascal equals one millibar, so weather reports can use either.
Should I convert gauge or absolute pressure?
Convert like with like. Tire pressure is gauge pressure; if a spec gives absolute pressure, subtract about 1 bar or 14.7 psi first.
What is 35 psi in bar?
2.41 bar, or 241 kPa. Most car tires run somewhere between 2.0 and 2.5 bar, so 35 psi sits right in that range.