PSI to Bar

Most passenger car tires run between 32 and 35 psi, which is roughly 2.2 to 2.4 bar. The right number is on the placard inside the driver's door jamb or in the owner's manual, not the maximum molded into the tire sidewall. Check it when the tires are cold, since driving warms the air and can add 2–4 psi.

Gas station pumps in North America show psi; in Europe they usually show bar, and many digital pumps switch between the two. A quick conversion avoids filling a tire to 32 bar, a number no pump will reach but a figure people do type in by mistake. Rough pairs worth memorizing: 30 psi ≈ 2.1 bar, 33 psi ≈ 2.3 bar, 36 psi ≈ 2.5 bar, 44 psi ≈ 3.0 bar.

Road bike tires are often inflated to 80–100 psi, about 5.5–6.9 bar, while mountain bikes may run 25–30 psi, around 1.7–2.1 bar. Air tools commonly need 90 psi, about 6.2 bar, at the tool. Pressure washers are rated in thousands of psi: 2,000 psi is 138 bar and 3,000 psi is 207 bar.

Most of these figures are gauge pressure, the amount above the surrounding air; engineers sometimes write psig to make that clear and psia for absolute pressure. Absolute pressure adds about 14.7 psi, or 1.013 bar, at sea level.

Divide by 15 and add 3.5% for a close estimate: 45 psi ÷ 15 = 3, plus 0.1 gives 3.1 bar, against the exact 3.10. The other direction is on bar to psi, and tire placards printed in kilopascals are covered on kPa to psi.