Tire Pressure PSI Calculator
Calculate how tire pressure changes with temperature using the gas law. Enter your PSI and the temperature change to see the new pressure. Free, with the formula shown.
Updated 2026-06-14 · Free · No sign-up · Runs privately in your browser
Show the formula & steps
How the Tire Pressure Calculator Works
This calculator shows how your tire pressure changes when the temperature changes. Enter your current PSI, the temperature when you filled the tire, and the new temperature, and it returns the corrected pressure along with the PSI change. It is ideal for the seasonal swings that trigger the low-pressure warning light on a cold morning.
The math uses the gas law, which relates pressure to absolute temperature, so the result is more precise than the common 1-PSI-per-10°F rule of thumb.
The Formula
Tire pressure gauges read gauge pressure, but the gas law works in absolute pressure (gauge + atmospheric). It also requires absolute temperature, so Fahrenheit is converted to the Rankine scale by adding 459.67.
New PSI = (PSI + 14.696) × (T2 absolute ÷ T1 absolute) − 14.696
where T absolute = temperature in °F + 459.67. The 14.696 is standard atmospheric pressure in PSI.
Worked Example
Suppose you set 32 PSI at 70°F and the temperature later drops to 30°F:
- T1 absolute = 70 + 459.67 = 529.67
- T2 absolute = 30 + 459.67 = 489.67
- New absolute = (32 + 14.696) × (489.67 ÷ 529.67) = 46.696 × 0.9245 = 43.17 PSI
- New gauge = 43.17 − 14.696 ≈ 28.5 PSI
A 40°F drop costs roughly 3.5 PSI, close to the rule-of-thumb estimate of about 4 PSI.
Quick Reference: Pressure vs Temperature
| Temperature change | Approx. PSI change (from 32 PSI) |
|---|---|
| −30°F | about −2.6 PSI |
| −20°F | about −1.8 PSI |
| −10°F | about −0.9 PSI |
| +10°F | about +0.9 PSI |
| +20°F | about +1.8 PSI |
Why It Matters
- Cold mornings can drop pressure enough to trigger the TPMS warning light even with no leak.
- Under-inflation hurts handling, fuel economy, and tire life, and can cause overheating.
- Set pressure cold to the value on the driver-door placard, then let normal driving warmth raise it.
Frequently asked questions
How does temperature affect tire pressure?+
Air pressure rises and falls with temperature. As a rule of thumb, tire pressure changes by about 1 PSI for every 10°F change in temperature, dropping in the cold and rising in the heat. This calculator uses the exact gas-law relationship for a precise figure.
How do I calculate the new tire pressure after a temperature change?+
Work in absolute pressure and temperature. Add 14.696 to your gauge PSI, multiply by the ratio of the new absolute temperature to the old (°F + 459.67), then subtract 14.696. For 32 PSI cooling from 70°F to 30°F, the new pressure is about 28.9 PSI.
Why must I use absolute temperature?+
Gas pressure is proportional to absolute temperature, not Fahrenheit or Celsius. You must convert °F to the Rankine scale by adding 459.67 (or °C to Kelvin by adding 273.15) before taking the ratio, or the math gives the wrong answer.
Should I set tire pressure when tires are cold?+
Yes. Vehicle pressure recommendations are for cold tires, meaning before driving or at least three hours after. Driving heats the air and raises the reading, so checking warm tires makes them look over-inflated.
Does this account for tires warming up while driving?+
It models the pressure change for any temperature difference you enter, including the air temperature rise from driving. Driving typically warms tires by 10°F to 40°F, raising pressure a few PSI, which is normal and why cold readings are the standard.