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How much does tire pressure change with the temperature?
Air in a tire reads higher when it's warm and lower when it's cool. Enter your door-sticker pressure, the temperature when you filled the tires and the temperature now to see the estimated reading by the common rule of thumb and by the gas law. Whatever the estimate says, set pressure cold, to the door placard.
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Pressure vs temperature
Why the tire light can come on during a cold-front morning, and why the reading is higher at 3 pm in July.
Try a Florida day
Filled at 78°F on a July morning in Miami, read again at 95°F that afternoon.
From the sticker in the driver's door jamb, not the maximum on the sidewall.
The air temperature when the tires were set, cold.
95°F
30°F to 110°F. Use the arrow keys for 1°F steps.
At 95°F, tires set to your door-sticker value of 35 PSI at 78°F would read about 36.6 PSI by the gas law, or 36.7 PSI by the rule of thumb. That's about 1.6 PSI higher than when the tires were filled at 78°F.
These are estimates of what a gauge would read, from air temperature alone. Sun on the tire, recent driving and your gauge all move the real number. Always set pressure to your door-sticker value with the tires cold.
Gas law Rule of thumb Door sticker
| Air temp | Rule of thumb | Gas law |
|---|---|---|
| 40°F | 31.2 PSI | 31.5 PSI |
| 50°F | 32.2 PSI | 32.4 PSI |
| 60°F | 33.2 PSI | 33.3 PSI |
| 70°F | 34.2 PSI | 34.3 PSI |
| 80°F | 35.2 PSI | 35.2 PSI |
| 90°F | 36.2 PSI | 36.1 PSI |
| 100°F (closest to now) | 37.2 PSI | 37.0 PSI |
| 110°F | 38.2 PSI | 38.0 PSI |
Just drove? Tires read higher when they're hot from driving. Don't let air out of a hot tire; check it after the car has been parked for 3+ hours.
Under FMVSS No. 138, the tire pressure warning light is designed to come on when a tire is 25% or more below the door-sticker value (or below a minimum the standard sets, whichever is higher). The light is a warning, not a gauge.
Sources: USTMA Tire Care Essentials (opens in a new tab); Tire Rack, Temperature and Tire Pressure (opens in a new tab); NHTSA TireWise (opens in a new tab); NHTSA, Tires in the Garage (opens in a new tab); NHTSA Summer Driving Tips (opens in a new tab); FMVSS No. 138 (TPMS) (opens in a new tab)
Text version of this demo
Shows how a tire's pressure rises and falls with air temperature, using both the common rule of thumb and the gas-law calculation. Set pressures cold, to the value on the vehicle's door placard.
Step by step
How to use it
- Enter the cold pressure from the sticker in the driver's door jamb, not the maximum on the sidewall.
- Enter the air temperature when the tires were last set, cold.
- Move the temperature-now slider, or try one of the Florida days.
- Check each tire with a gauge when it's cold. If one reads below the placard, add air.
Questions
The things people ask next
How much does tire pressure change per 10 degrees?
USTMA and Goodyear put it at one to two psi for every 10°F, and Bridgestone says about 1 psi. The gas-law estimate for a typical passenger tire lands a little under 1 psi per 10°F.
Should I let air out when the tires read high on a hot day?
No. NHTSA's guidance is that pressure rises as tires warm, and letting air out of a warm tire can leave it low once it cools. Recheck after the car has been parked for three hours or more.
Why did the tire pressure light come on on a cool morning?
As the air cools, so does the pressure. A tire that was already a little low can drop far enough overnight to trigger the light. Set all four to the placard pressure, cold, even if the light goes out as the day warms up.
What counts as a cold tire?
NHTSA defines cold as parked for at least three hours, so first thing in the morning is the easiest time to check.
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