Pressure Converter
Units and exact values
The pascal (Pa) — one newton per square metre — is the SI unit of pressure. It is very small, so everyday pressures are given in larger units:
| Unit | In pascals | Typical use |
|---|---|---|
| 1 millibar (mbar) = 1 hPa | 100 Pa | Weather forecasts |
| 1 kilopascal (kPa) | 1,000 Pa | Tyres (Canada, Australia), engineering |
| 1 bar | 100,000 Pa | Tyres and pumps in Europe |
| 1 standard atmosphere (atm) | 101,325 Pa | Physics, diving |
| 1 psi (pound per square inch) | 6,894.76 Pa | Tyres and tools in the US/UK |
| 1 mmHg | 133.32 Pa | Blood pressure |
Worked examples
- Car tyres: 2.2 bar = 2.2 × 100,000 ÷ 6,894.76 = 31.9 psi. Most cars run between 2.0 and 2.6 bar (29–38 psi); the correct value is on a sticker inside the driver's door or fuel flap.
- Weather: standard sea-level pressure is 1,013.25 hPa = 1 atm = 14.7 psi. Readings below about 1,000 hPa usually mean unsettled weather.
- Blood pressure: 120 mmHg = 16.0 kPa.
Gauge vs absolute pressure
A tyre gauge shows pressure above atmospheric pressure (gauge pressure, sometimes written psig or barg). A flat tyre reads 0 even though the air inside is at about 1 bar absolute. Scientific data often uses absolute pressure — add about 1.013 bar (14.7 psi) to convert gauge to absolute.
Quick estimate: 1 bar ≈ 14.5 psi ≈ 1 atm. For tyre pressures, multiply bar by 14.5 to get psi.
Frequently Asked Questions
How many psi is 1 bar?
1 bar is 14.504 psi. One psi is 0.0689 bar.
What tyre pressure should I use?
Use the value recommended by your car manufacturer, printed on a sticker in the door frame or fuel flap and in the owner's manual, and check it when the tyres are cold.
Are millibars and hectopascals the same?
Yes. 1 mbar = 1 hPa = 100 Pa, which is why weather services can use either unit.