Tire Pressure Temperature Calculator
This tire pressure temperature calculator shows how pressure follows the air temperature: 35 psi set at 70 °F drops to about 31.2 psi at 30 °F. It also tells you what to inflate to in a warm garage so the tires are right outside.
Example: Tire pressure (gauge) 35 · Unit: psi · Temperature when measured 70 · New temperature 30 · Temperature unit: °F → Tire pressure: At 30 °F: 31.2 psi (−3.8 psi). Source: OpenStax, College Physics 2e, 13.3 The Ideal Gas Law – example “Calculating Pressure Changes Due to Temperature Changes: Tire Pressure” (P_f = P_0 · T_f/T_0, absolute pressure and temperature; 7.00 × 10⁵ Pa at 18 °C → 7.41 × 10⁵ Pa at 35 °C) (read 10.10.2026). Updated: .
How it is calculated
New pressure = (gauge pressure + atmospheric pressure) × T new ÷ T old − atmospheric pressure, with temperatures in kelvin. This is the ideal gas law at constant volume: absolute pressure rises in the same ratio as absolute temperature. A tire gauge shows gauge pressure, the pressure above the outside air, so the calculator adds 14.70 psi (1 atm) first and subtracts it at the end.
The OpenStax physics textbook works through a bicycle tire: 7.00 × 10⁵ Pa absolute at 18 °C becomes 7.41 × 10⁵ Pa at 35 °C, about 6 % more. It also notes that most manufacturers specify tire pressure for cold tires.
Tire pressure chart for 35 psi set at 70 °F
| Temperature | Tire pressure |
|---|---|
| 10 °F | 29.4 psi |
| 30 °F | 31.2 psi |
| 50 °F | 33.1 psi |
| 90 °F | 36.9 psi |
At 35 psi the pressure changes by about 0.94 psi for every 10 °F, a little under 1 psi. With higher pressures the change is slightly larger because the absolute pressure is higher.
Warm garage, cold morning
- To have 35 psi at 30 °F outside, inflate to about 39.1 psi in a 70 °F garage.
- After driving, tires are warmer than the air, so the gauge reads more than the cold pressure.
- The calculation assumes no air escapes and the tire volume stays the same.
Convert units with the bar to psi converter; the general gas law is in the ideal gas law calculator.
Frequently asked questions
How much does tire pressure drop in cold weather?
At 35 psi about 0.94 psi per 10 °F. From 70 °F to 30 °F the pressure falls from 35 to about 31.2 psi.
Should I add air when it gets cold?
The placard value is for cold tires. If you inflate in a warm garage, the tires will be lower outside. For 35 psi at 30 °F, set about 39.1 psi at 70 °F.
Why use absolute pressure?
The gas law applies to absolute pressure. A gauge reads pressure above the atmosphere, so 14.70 psi is added before and subtracted after the calculation.
Does tire pressure go up when driving?
Yes, because the air inside warms up. Check pressure cold, before driving or after the car has been parked for a while.
How much does pressure change per degree?
At 35 psi about 0.094 psi per °F: the absolute pressure of about 49.7 psi changes by 1/530 for each degree Fahrenheit at 70 °F.
Sources and legal basis
- OpenStax, College Physics 2e, 13.3 The Ideal Gas Law – example “Calculating Pressure Changes Due to Temperature Changes: Tire Pressure” (P_f = P_0 · T_f/T_0, absolute pressure and temperature; 7.00 × 10⁵ Pa at 18 °C → 7.41 × 10⁵ Pa at 35 °C) (read 10.10.2026)
- NIST SP 811, Appendix B.8: 1 atm = 101.325 kPa, 1 bar = 100 kPa, 1 psi = 6.894 757 kPa (read 10.10.2026)
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