What conversion factors are used for tire pressure units?

Per NIST SP 811: 1 bar equals exactly 100 kPa; 1 psi equals 6.894757 kPa (0.06894757 bar); and 1 kgf/cm² equals exactly 98.0665 kPa (0.980665 bar or 14.2233 psi). So 32 PSI is 2.206 bar or 220.6 kPa, and 2.5 bar is 36.26 PSI.

How much does tire pressure change with temperature?

About 1 PSI for every 10 °F (roughly 1.2 kPa or 0.012 bar per °C) for a typical car tire. The exact change follows the gas law on absolute pressure: a tire set to 35 PSI at 70 °F reads about 31.2 PSI at 30 °F, because (35 + 14.7) × 272.0 K ÷ 294.3 K − 14.7 = 31.2. Higher pressures change slightly more per degree than lower ones.

What is the difference between gauge pressure (psig) and absolute pressure (psia)?

A tire gauge reads gauge pressure, the pressure above the surrounding atmosphere. Absolute pressure adds the atmosphere back: at sea level 32 psig is about 46.7 psia (220.6 kPa gauge is 322.0 kPa absolute). Placards and pump gauges always use gauge pressure, but temperature corrections must be done on absolute pressure.

Where should I look to find my vehicle correct tire pressure?

Use the placard on the driver door jamb, pillar or fuel filler door, or the owner manual. The pressure on the tire sidewall is the maximum the tire can hold, not the vehicle maker recommendation. Bicycle tires are the exception: the sidewall prints a recommended minimum to maximum range.

When is a tire considered cold for accurate pressure measurement?

According to NHTSA TireWise guidance, measure pressure when the tires are cold, meaning the vehicle has not been driven for at least three hours. Driving heats the air inside the tire and raises the reading; never let air out of a hot tire to match the cold placard number.

At what pressure does the TPMS warning light come on?

FMVSS 138 requires a US tire pressure monitoring system to warn when a tire is 25% or more below the cold placard pressure, or below a minimum activation pressure set in the standard, whichever is higher. For a 35 PSI placard the 25% point is 26.25 PSI.

Are kg/cm² and bar the exact same unit?

No. 1 kgf/cm² is 98.0665 kPa (0.980665 bar), so 1 bar is about 1.97% greater than 1 kgf/cm². At 2.2 the difference is about 0.04 bar or 0.6 PSI.

Tire Pressure Converter

Convert tire pressure between PSI, bar, kPa and kgf/cm² with exact NIST factors, then predict how the reading changes with temperature (about 1 PSI per 10 °F) using the gas law on absolute pressure.

Pressure Unit Converter

Enter a value in any unit. All fields synchronize instantly.

Quick Entry Values (Not Recommendations)

Choose only a value shown on your vehicle placard or owner manual.

PSI (lbf/in²)

PSI

bar (100 kPa)

bar

kPa (kilopascals)

kPa

kgf/cm² (technical atmosphere)

kgf/cm²

Gauge Neighbor Stepping Chart

Values ±5 PSI around active setting for quick air pump dial alignment.

PSI	bar	kPa	kgf/cm²

Temperature Correction & TPMS Point

Predict the gauge reading at another temperature (ideal gas law on absolute pressure, same tire volume).

Gauge reading

Temp at reading

New temp

Temperature unit

Air pressure outside (kPa)

—

Use a lower outside air pressure at altitude (about 84 kPa at 5,000 ft); it changes the result only slightly. The gas law ignores the small stretch of the tire casing, so treat the result as an estimate within a few tenths of a PSI.

Typical Cold Pressure Ranges

Broad ranges to sanity-check a number. Your door placard (or, for bicycles, the sidewall range) is the spec to use.

Vehicle / tire	PSI	bar	kPa
Passenger car	30–36	2.1–2.5	207–248
SUV / crossover (P-metric)	32–40	2.2–2.8	221–276
Light truck, LT load range E	50–80	3.4–5.5	345–552
Motorcycle	28–42	1.9–2.9	193–290
Road bike, 25–32 mm	60–100	4.1–6.9	414–689
Hybrid / commuter bike	50–70	3.4–4.8	345–483
Mountain bike, tubeless	20–35	1.4–2.4	138–241

Unit Equivalents & Scientific Ratios

Calculations conform to National Institute of Standards and Technology (NIST SP 811) SI conversion standards:

1 bar = 100 kPa (exact)

1 bar ≈ 14.503774 PSI

1 PSI = 6.894757 kPa

1 kgf/cm² = 98.0665 kPa (exact)

Safety Limitations & Cold Pressure Guidelines

Placard vs. Sidewall: Always inflate to the pressure specified on your vehicle door jamb or owner manual. The number stamped on the tire sidewall is the tire maximum permissible inflation pressure, not the vehicle manufacturer recommendation.
Cold Definition (NHTSA): Measure pressure when tires are cold—defined by NHTSA TireWise as not having been driven for at least three hours.
Axle & Load Variances: Do not rely on generic charts. Front and rear axle specifications frequently differ based on vehicle weight distribution and towing conditions.

Summary

This converter turns a tire pressure reading into PSI (pounds-force per square inch), bar, kPa and kgf/cm² using NIST SP 811 factors (1 psi = 6.894757 kPa, 1 bar = 100 kPa, 1 kgf/cm² = 98.0665 kPa). Tire gauges read gauge pressure, the pressure above the surrounding air, so the tool also shows the absolute value (gauge + 14.696 psi at sea level). The temperature panel applies the ideal gas law to absolute pressure, P₂ = (P₁ + Patm) × T₂ / T₁ − Patm with T in kelvin. For a car tire that works out to roughly 1 PSI for every 10 °F (about 1.2 kPa per °C). The correct cold pressure for your vehicle is on the door-jamb placard or in the owner manual, not on the tire sidewall.

How it works

Type a value in any of the four unit fields (PSI, bar, kPa, kgf/cm²); the other three update instantly.
The result cards also show absolute pressure: gauge pressure plus one standard atmosphere (14.696 psi, 101.325 kPa).
In the temperature panel, enter a reading, the temperature it was taken at and a target temperature to predict the new reading. The tool converts to absolute pressure and kelvin, scales by T₂/T₁, then converts back to gauge.
The same panel shows the FMVSS 138 TPMS warning point (25% below the cold placard pressure) for the value entered.
Use the ±5 PSI step chart to match nearby gauge marks, and the typical-range table to sanity-check a spec.

Use cases

Converting a European door placard in bar (for example 2.3 bar) to a PSI air pump gauge (33.4 PSI).
Translating Japanese or Korean kPa specifications (for example 240 kPa) into PSI (34.8) or bar.
Working out what a tire set to 35 PSI in a 70 °F garage will read on a 30 °F morning (about 31.2 PSI).
Deciding how much extra to add when inflating in a warm shop before cold-weather driving.
Checking an old kgf/cm² gauge against a bar or PSI placard (1 kgf/cm² is 1.97% less than 1 bar).
Finding the pressure at which a TPMS light must come on for a given placard value.

Frequently Asked Questions

Last updated: 2026-10-10 · Reviewed by Nham Vu