Pressure Unit Converter
Pressure is force spread over an area, and four unit systems are in common use for it at once. This converter moves between them, and the notes below cover the gauge-versus-absolute distinction that causes more trouble than the arithmetic.
Formula
pascals = value × the factor for its unit
- 1 bar = 100,000 Pa
- 1 PSI = 6,894.76 Pa
- 1 atm = 101,325 Pa
32 PSI in a tyre is 2.21 bar, or 220.6 kPa
The Units and Where Each Is Used
The pascal is the SI unit and is inconveniently small — one newton over one square metre, roughly the pressure of a sheet of paper lying flat. Everything else is a practical multiple:
- 1 kPa = 1,000 Pa
- 1 bar = 100 kPa, chosen to sit close to atmospheric pressure
- 1 atm = 101.325 kPa exactly — standard atmospheric pressure by definition
- 1 PSI = 6.89476 kPa, and 1 bar = 14.5038 PSI
A bar and an atmosphere are close but not equal: a bar is about 1.3% less. Meteorology uses the millibar, now formally the hectopascal, which is why a weather chart reads around 1013 hPa at sea level.
Gauge Versus Absolute
This distinction matters more than any conversion factor, and it is the one most often skipped.
A tyre gauge reads zero against open air, so it is measuring pressure above atmospheric. That is gauge pressure, written PSIG. Absolute pressure counts from a vacuum and includes the atmosphere pressing in, written PSIA.
A tyre at 32 PSI gauge is at 32 + 14.7 = 46.7 PSI absolute.
For tyres and most workshop work, gauge is the useful figure and the difference can be ignored. In gas law calculations, compressor sizing and diving, it cannot: using gauge pressure where absolute is required is a genuine and occasionally dangerous error.
Tyre Pressures in Practice
Most car tyres want 30–35 PSI, which is 2.1–2.4 bar or 207–241 kPa. Continental European placards usually quote bar, so 2.2 bar on a door sticker is 32 PSI.
Two practical notes. Check pressures cold, because driving heats the air and adds a few PSI, and a "correct" reading on a hot tyre means it is under-inflated once it cools. And pressure falls with temperature at roughly 1 PSI for every 5.5°C, which is why the warning light tends to appear on the first cold morning of autumn rather than because anything has gone wrong.
Quick Reference
| Context | PSI | Bar | kPa |
|---|---|---|---|
| Sea level atmosphere | 14.7 | 1.014 | 101.4 |
| Car tyre, lower end | 30 | 2.068 | 206.8 |
| Car tyre, typical | 32 | 2.206 | 220.6 |
| Car tyre, loaded | 35 | 2.413 | 241.3 |
| Pressure washer | 100 | 6.895 | 689.5 |
Frequently Asked Questions
- How many PSI are in a bar?
- 14.5038 PSI. Going the other way, 1 PSI is 0.0689476 bar.
- Is 1 bar the same as 1 atmosphere?
- Almost. A bar is 100 kPa and an atmosphere is 101.325 kPa, so an atmosphere is about 1.3% higher.
- What is the difference between gauge and absolute pressure?
- Gauge pressure is measured relative to the surrounding air, so it reads zero in the open. Absolute pressure counts from a vacuum and is about 14.7 PSI higher at sea level.
- What pressure should my car tyres be?
- Typically 30 to 35 PSI, or 2.1 to 2.4 bar, but the placard in the door frame or fuel flap gives the figure for your car and load. Check them cold.