FLATFIXVAULT · FORT LAUDERDALE · FREE TOOL
For fleet operators and drivers. Enter your real cold tire PSI and a new ambient temperature — get the exact pressure change using Gay-Lussac’s Law, not a guess.
Tire pressure changes with ambient air temperature because the air sealed inside the tire follows the gas laws. As a rough rule of thumb, tire pressure changes by about 1 PSI for every 10°F change in ambient temperature. This calculator computes the exact figure using Gay-Lussac’s Law instead of the rough rule of thumb.
Gay-Lussac’s Law states that for a fixed volume of gas, pressure divided by absolute temperature is constant (P1/T1 = P2/T2). This calculator converts your entered PSI to absolute pressure (PSIA = PSIG + 14.7) and both temperatures to absolute Rankine (°F + 459.67), applies the law, then converts the result back to a normal gauge PSI reading.
No. This calculator only models the effect of a change in ambient air temperature — for example, a cold morning versus a hot afternoon. It does not model the additional pressure increase caused by tire flexing and friction heat during driving, which is a separate effect and can add several more PSI after sustained highway driving.
The correct cold tire pressure for your vehicle is printed on the placard inside the driver’s door jamb, or in your owner’s manual. It is not the number printed on the tire’s own sidewall — that number is the tire’s maximum pressure rating, not the recommended operating pressure for your vehicle.
No. Always set your cold tire pressure to match your vehicle’s door-jamb placard using a real gauge. This tool is informational only, to help you understand how much a temperature swing will move your PSI reading — it does not replace checking and setting pressure against your placard spec.