About this tool
Tire Pressure Temperature Calculator is a free, in-browser tool that predicts what your tire pressure will read after a change in temperature — for instance the drop you see on a cold morning or the rise after a hot highway run. Enter the pressure you set, the temperature when you set it, the new temperature and the unit; the result is computed locally with nothing uploaded.
The physics is Gay-Lussac's law (pressure is proportional to absolute temperature at fixed volume), applied to absolute pressure. Temperatures are converted to an absolute scale — °F to Rankine (°F + 459.67) and °C to Kelvin (°C + 273.15) — and gauge pressure is converted to absolute by adding 14.7 psi of atmosphere. The new gauge pressure is P2 = (P1 + 14.7) × (T2abs ÷ T1abs) − 14.7. The tool also shows the popular field shortcut of about 1 psi per 10 °F of change, so you can see how the rule of thumb compares to the exact figure.
Use it to know whether to add or bleed air after the weather shifts, or to understand why your TPMS light comes on during the first cold snap. Because pressure follows absolute temperature, a swing that looks small in °F still moves your tires by a meaningful amount — always set and check pressures when the tires are cold.