Which pressure unit is used where
- psi: US tires (30–35 psi on most cars), air compressors, hydraulics.
- bar: European tire gauges, scuba tanks (200–300 bar), espresso machines (9 bar).
- kPa: the SI unit you see on tire placards next to psi; 1 bar = 100 kPa.
- inHg: barometers and aircraft altimeters (29.92 inHg = 1 standard atmosphere). mmHg: blood pressure. Torr: vacuum pumps.
- m of water (mH₂O): pump head; every 10 m of water column is about 1 bar. kgf/cm²: older gauges, nearly equal to 1 bar.
1 psi = 6,894.757 Pa = 0.06894757 bar 1 bar = 14.50377 psi
1 atm = 101,325 Pa (exact) = 1.01325 bar = 14.6959 psi
1 mmHg = 133.322 Pa 1 Torr = 1/760 atm = 133.3224 Pa
1 mH₂O = 9,806.65 Pa 1 kgf/cm² = 98,066.5 Pa = 0.980665 bar
psi to bar conversion chart
| psi | bar | kPa | kgf/cm² |
|---|---|---|---|
| 14.7 psi | 1.014 | 101.4 | 1.034 |
| 25 psi | 1.724 | 172.4 | 1.758 |
| 30 psi | 2.068 | 206.8 | 2.109 |
| 32 psi | 2.206 | 220.6 | 2.25 |
| 35 psi | 2.413 | 241.3 | 2.461 |
| 40 psi | 2.758 | 275.8 | 2.812 |
| 50 psi | 3.447 | 344.7 | 3.515 |
| 90 psi | 6.205 | 620.5 | 6.328 |
| 100 psi | 6.895 | 689.5 | 7.031 |
| 120 psi | 8.274 | 827.4 | 8.437 |
| 150 psi | 10.34 | 1,034 | 10.55 |
Worked example
A European car door sticker says 2.4 bar. In psi: 2.4 × 14.5038 = 34.8 psi, so inflate to 35 psi. Gauge pressure (what tire gauges show) is measured above atmospheric pressure; absolute pressure adds about 14.7 psi (1.013 bar).
Frequently asked questions
How many psi is 1 bar?
1 bar = 14.504 psi. To convert bar to psi, multiply by 14.5038; for psi to bar, divide by it (or multiply by 0.0689476).
What is 32 psi in bar?
32 psi = 2.206 bar = 220.6 kPa, a typical car tire pressure.
What is the difference between psi and psig?
psig is gauge pressure (above atmosphere), what a tire gauge reads. psia is absolute pressure, about 14.7 psi higher at sea level.