Bar to PSI for Tire Pressure: Exact Conversion, Table and Placard Example

One bar is 14.504 psi, and one psi is 0.06895 bar. Tire placards, pumps and gauges mix the two freely (plus kilopascals, which many placards print first), so a driver often has to turn "230 kPa" or "2.3 bar" into a psi figure on a gas-station pump, or the other way round. This guide gives the exact factor, a conversion table for the range tire gauges cover, a worked example using a typical placard figure, and the two things that trip people up: gauge versus absolute pressure, and hot versus cold tires.

The exact conversion

Both units have fixed definitions, so the factor between them is exact, even if its decimals run on:

• 1 bar = 100,000 pascals = 100 kPa (by definition).
• 1 psi = one pound-force per square inch = 6,894.757 Pa. This comes from the exact definitions of the pound-force and the inch.
• bar to psi: psi = bar × 14.5038 (more precisely 14.503774).
• psi to bar: bar = psi × 0.0689476, or psi ÷ 14.5038.
• kPa to psi: psi = kPa ÷ 6.894757. kPa to bar: divide by 100.

For tires, multiplying by 14.5 is close enough for mental math: it is 0.03% low, which is 0.01 psi at 2.3 bar. Your gauge cannot show a difference that small. What matters far more is the gauge itself. A bar gauge that reads in 0.1 bar steps resolves 1.45 psi per step, and one with 0.05 bar steps resolves 0.73 psi. Neither unit is "more precise"; the instrument is.

Bar to psi and kPa conversion table

Values computed from the exact definitions and rounded to 0.1 psi. These are unit conversions only, not recommended pressures.

And the reverse, for pumps that read in psi:

Reading the placard

The figure you want is on the Tire and Loading Information label. NHTSA says it is on the driver's side door edge and in the owner's manual. The federal labeling rule (FMVSS 110) requires the placard on the driver's side B-pillar, the door jamb post. On cars without one, it goes on the forward edge of the rear side door, the rear edge of the driver's door, or a surface next to the driver's seat. On older vehicles, NHTSA's brochure also mentions the glove-box door or the inside of the trunk lid. The placard lists a cold pressure for the front and rear tires, which may differ, and sometimes a second set for a fully loaded vehicle.

US placards give psi and usually kPa as well. NHTSA's tire safety brochure notes that the kPa figure is the metric unit used internationally. Placards on cars built for other markets may give kPa or bar instead. All three describe the same pressure, so pick the unit your gauge reads and convert only if you have to.

The sidewall number is different. The sidewall shows the maximum pressure the tire can hold, for example "Max. Press. 300 kPa (44 psi)". Tire Rack gives 300 kPa (44 psi) and 350 kPa (51 psi) as examples of passenger-tire sidewall maximums. NHTSA is explicit that the correct pressure is the one the vehicle manufacturer lists, not the number on the tire. The maximum is a ceiling, never a target.

There is no single "normal" figure to copy: vans, SUVs with heavy loads and cars with low-profile tires can be quite different, and front and rear can differ on the same car. Check your placard.

Worked example: a placard in kPa, a pump in psi

The placard on a European hatchback says 230 kPa front and rear. The air pump at the gas station is set in psi.

1. Convert kPa to psi: 230 ÷ 6.894757 = 33.36 psi.
2. Cross-check through bar: 230 kPa = 2.3 bar, and 2.3 × 14.5038 = 33.36 psi. The two routes agree.
3. Pumps usually step in whole psi, so set 33 psi (2.28 bar), the nearest whole number: it is 0.36 psi below the placard figure. 34 psi (2.34 bar) would be 0.64 psi above it. Both are smaller than the 1.45 psi step of a gauge that reads in 0.1 bar.
4. Check the result with your own gauge after inflating, so you know both readings agree.

Going the other way: a US placard says 35 psi and your gauge reads bar. 35 × 0.0689476 = 2.41 bar, or 241 kPa. On a gauge with 0.1 bar steps, aim for 2.4 bar.

Gauge pressure vs absolute pressure

A tire gauge reads gauge pressure: how far the air inside the tire is above the air around it. A flat tire still holds air at atmospheric pressure, yet the gauge shows zero. Absolute pressure counts from a perfect vacuum, so it adds the atmosphere (about 1.013 bar or 14.7 psi at sea level) on top.

Engineers mark the difference with "psig" (gauge) and "psia" (absolute). For example, a tire at 65 psig is at 79.7 psia at sea level (65 + 14.7). Every tire placard, pump and handheld gauge uses gauge pressure, so you never add or subtract the atmosphere when converting a tire figure. The factor 14.5038 is all you need.

The confusion is worth avoiding because the error is large. If someone treated a 2.2 bar placard as absolute and subtracted the atmosphere, they would end up near 17 psi on the gauge instead of 31.9 psi, which is badly under-inflated. For a deeper look at gauge and absolute readings in weather, diving and lab work, see our guide to pressure units from pascals to psi.

Hot vs cold: when to check

Placard pressures are cold pressures. NHTSA defines a cold tire as one that has not been driven for at least three hours; it has nothing to do with the weather. Driving warms the air inside, and warm air at the same volume pushes harder. In a Tire Rack test on a tire test machine, pressure rose about 1 psi for every 5 minutes of running during the first 20 minutes, then gained no more than about 1 psi over the next 20.

Outside temperature matters too. Tire Rack puts the change at about 2% for every 10 °F, which is roughly 1 psi for a passenger tire. The chart below shows the ideal-gas estimate for a tire set at 2.3 bar in a 20 °C garage.

This is why a tire that was already a little low in September can trigger the low-pressure light on the first cold morning of winter. In the US, FMVSS 138 requires the tire pressure monitoring system on light vehicles (10,000 lb GVWR or less, fully required from September 2007) to light the warning within 20 minutes once a tire is 25% or more below the placard pressure, or below a fixed minimum (140 kPa, about 20 psi, for standard passenger tires), whichever is higher. For a 35 psi placard that is about 26 psi, which is already well under-inflated. NHTSA says the TPMS is not a substitute for checking pressure with a gauge at least once a month.

Using the SamemaS pressure converter

The pressure converter shows pascal, kilopascal, megapascal, bar, atmosphere, psi, torr and mmHg at once. Type a value into any field and the others update in your browser. It converts the number you give it and has no gauge or absolute setting, so a gauge figure in gives a gauge figure out, which is exactly what you want for tires. If you are also checking outside temperatures in °F and °C for the hot and cold rule, the temperature converter does that.

Quick checklist

• Find your cold pressure on the placard (door jamb or door edge) or in the owner's manual.
• Convert: psi = bar × 14.5038; bar = psi × 0.0689; kPa = bar × 100.
• All tire figures are gauge pressure. Never add or subtract 14.7 psi.
• Check cold (parked three hours or more) and at least once a month, spare included.
• Never inflate above the sidewall maximum; it is a limit, not a target.
• Don't let air out of hot tires to match the placard.

Frequently asked questions

Sources

1. Tires: Tire Safety Ratings and Awareness — National Highway Traffic Safety Administration
2. Tire Safety: Everything Rides on It (brochure) — National Highway Traffic Safety Administration
3. What Are North American Load/Pressure Markings? — Tire Rack
4. How Does Temperature Change Affect Tire Air Pressure? — Tire Rack
5. 49 CFR 571.138: Tire pressure monitoring systems (FMVSS 138) — U.S. Code of Federal Regulations
6. 49 CFR 571.110: Tire selection and rims (FMVSS 110) — U.S. Code of Federal Regulations