PSI and Bar explained
PSI is force in pounds divided by area in square inches, and it is the pressure unit of American engineering and of tyre placards on cars sold in the US. The bar is metric but not SI — it is defined as exactly 100,000 pascals, which is close to average atmospheric pressure at sea level (101,325 Pa, or 1.01325 bar). European car manuals, bicycle tyres and espresso machines are all specified in bar. The important distinction is gauge versus absolute pressure: a tyre gauge reading 32 psi means 32 psi above atmospheric, so the absolute pressure inside the tyre is about 46.7 psi. Nearly every practical pressure specification is a gauge reading.
Formula and worked examples
bar = psi × 0.0689476Multiply psi by 0.0689476, or divide by 14.5038. A typical car tyre at 32 psi is 2.21 bar. A road bike at 100 psi is 6.89 bar. An espresso machine brewing at 9 bar is running at 130.5 psi. One standard atmosphere, 14.696 psi, is 1.013 bar — which is why "1 bar" and "1 atmosphere" are used loosely as synonyms even though they differ by 1.3%.
PSI to Bar conversion table
Common PSI values converted to Bar. Every figure uses the same conversion factor as the calculator above.
| PSI | Bar |
|---|---|
| 1 | 0.06894757 |
| 2 | 0.13789514 |
| 5 | 0.34473785 |
| 10 | 0.6894757 |
| 20 | 1.3789514 |
| 50 | 3.4473785 |
| 100 | 6.894757 |
Where you will use this
Setting car tyre pressure
A car built for the European market lists 2.2 bar on the door placard while the compressor at the service station reads psi. 2.2 bar is 31.9 psi, so the 32 psi setting on the pump is correct.
Inflating bicycle tyres
Tyre sidewalls often print both units but pumps rarely do. A gravel tyre rated 40–70 psi is 2.76–4.83 bar, and knowing the bar equivalent matters when the only gauge you have is a metric floor pump.
Espresso and machine specifications
Espresso extraction is standardised at 9 bar, and pump specifications are quoted as 15 bar. In psi those are 130.5 and 217.6, the figures you need when comparing against a US-market machine.