PSI and bar both measure pressure, and converting between them is a single multiplication — but the number on your gauge depends on whether it reads relative to the atmosphere or to a vacuum. This guide gives the exact factor, a table for the values people actually look up, and explains when the difference between gauge and absolute pressure changes the answer.
The conversion
1 bar = 14.5037738 psi, and 1 psi = 0.0689476 bar.
For mental arithmetic, 1 bar ≈ 14.5 psi is close enough for anything outside a calibration lab. Going the other way, 1 psi ≈ 0.069 bar, so 100 psi ≈ 6.9 bar — a figure worth memorising if you work with compressed air.
Worked example: a tyre placard says 35 psi. In bar that is 35 × 0.0689476 = 2.41 bar. European cars usually show 2.4 bar for the same tyre — the difference is rounding, not a different recommendation.
Reference table
| PSI | Bar | Where you see it |
|---|---|---|
| 1 psi | 0.069 | Low-pressure gas signal |
| 14.7 psi | 1.013 | Standard atmospheric pressure at sea level |
| 20 psi | 1.38 | Low-pressure propane regulator |
| 32 psi | 2.21 | Compact car tyre |
| 35 psi | 2.41 | Most passenger car tyres |
| 44 psi | 3.03 | Loaded SUV / light truck tyre |
| 90 psi | 6.21 | Truck tyre |
| 100 psi | 6.89 | Typical shop air line |
| 150 psi | 10.34 | Industrial compressor tank |
| 3000 psi | 206.8 | SCUBA / paintball tank |
You can check any of these with the Pressure Converter, which also handles kPa, MPa and atmospheres.
Gauge pressure versus absolute pressure
This trips people up more than the unit conversion itself. A gauge reads pressure relative to ambient air, so at sea level a gauge showing zero is actually sitting under 14.7 psi (1.013 bar) of atmosphere. Absolute pressure adds that back in.
The notation tells you which one you have: psig (gauge) versus psia (absolute), and barg versus bara. A compressor tank at 100 psig holds about 114.7 psia. For filling tyres, inflating a ball, or setting a regulator, gauge pressure is what you want — the atmosphere pushes back on both sides, so it cancels out. Absolute pressure matters in vacuum work, gas law calculations, and altitude-corrected processes, where the atmosphere does not cancel.
Why tyre pressures look different by market
The same vehicle sold in the US and Europe carries a placard in psi in one market and bar in the other, and the numbers are rounded differently: 35 psi becomes 2.4 bar, 33 psi becomes 2.3 bar. Neither is more accurate — they are the same target pressure rounded to the precision each market expects. Setting your tyres to “2.4” on a US gauge calibrated in psi (by converting back to 35) is correct; reading 2.4 as “2.4 psi” would leave the tyre dangerously under-inflated.
Check tyres cold — before driving, or at least three hours after. Driving heats the air inside and raises the reading by 3–5 psi, which is normal and should not be bled off.
Other pressure units you will meet
Bar and psi are not the only options, and knowing the neighbours saves time:
- kPa (kilopascal): the metric standard used in weather reports and most non-US engineering. 1 bar = 100 kPa exactly, and standard atmospheric pressure is 101.325 kPa.
- MPa (megapascal): used for high-pressure hydraulics and material strength. 1 MPa = 10 bar = 145 psi.
- atm (atmosphere): defined as 101,325 Pa, so 1 atm = 1.01325 bar = 14.696 psi. Useful in chemistry and gas calculations.
- mmHg / Torr: used in medical and vacuum contexts. 1 atm = 760 mmHg.
Converting via bar is usually the simplest route: kPa and bar differ by a factor of exactly 100, which makes mental conversion trivial. Going from a weather report in kPa to a tyre gauge in psi, divide by 100 to get bar, then multiply by 14.5 — a 101 kPa day is 1.01 bar, or about 14.7 psi of atmospheric pressure.
Key Takeaways
1 bar = 14.5038 psi and 1 psi = 0.0689476 bar; for quick work use 1 bar ≈ 14.5 psi and 100 psi ≈ 6.9 bar. A 35 psi tyre is 2.41 bar. Always check whether a figure is gauge (psig/barg) or absolute (psia/bara) — they differ by one atmosphere, about 14.7 psi, and mixing them up is a far bigger error than any rounding in the conversion.