Tire Pressure Temperature Calculator
Estimate how much your tire pressure will rise or fall with a temperature change. Enter the current gauge pressure, both temperatures and the local atmospheric pressure to get the new pressure instantly.
Estimate Tire Pressure After a Temperature Change
Tire Pressure Temperature Formula
Where:
- \(P_1\) — current tire pressure, gauge reading (psi, bar, kPa or kg/cm²)
- \(P_{atm}\) — local atmospheric pressure, in the same unit as \(P_1\)
- \(T_1\) — current temperature, converted to kelvin
- \(T_2\) — expected temperature, converted to kelvin
- \(P_2\) — gauge pressure at the new temperature
This is Gay-Lussac's law applied to a fixed volume of air: at constant volume, absolute pressure is proportional to absolute temperature. Because a tire gauge reads pressure above atmospheric, the atmospheric pressure must be added before the ratio is taken and subtracted again afterwards.
Tire Pressure Temperature – Calculation Example
Example: a tire is inflated to 32 psi (gauge) on a mild day at 20 °C. Overnight the temperature drops to −10 °C, and the local atmospheric pressure is 14.7 psi (sea level). First convert the temperatures to kelvin: \(T_1 = 293.15\) K and \(T_2 = 263.15\) K.
\[ P_1^{abs} = 32 + 14.7 = 46.7 \ \text{psi} \]
\[ P_2^{abs} = 46.7 \times \frac{263.15}{293.15} \approx 41.92 \ \text{psi} \]
\[ P_2 = 41.92 - 14.7 \approx 27.2 \ \text{psi} \]
Result: the gauge pressure falls to about 27.2 psi (187.7 kPa) — a drop of 4.8 psi overnight. These are exactly the calculator's default values, so you can reproduce the result with one click.
How to use the calculator
- Enter your Current tire pressure (P₁) — the reading from your tire gauge — and choose its unit (psi, bar, kPa or kg/cm²).
- Enter the Current air temperature (T₁), i.e. the temperature at which that pressure was measured, and pick °C, °F or K.
- Enter the Expected air temperature (T₂) the tires will be exposed to, such as an overnight frost or a hot summer afternoon.
- Enter the Atmospheric pressure (P atm) for your location. The default 14.7 psi (101.3 kPa) is the standard sea-level value; use a lower figure at high altitude. You can enter it in psi, inHg, kPa, bar or mmHg.
- Read the results: the approximate gauge pressure P₂ at the new temperature (shown in psi, bar, kPa and kg/cm²) and the pressure change ΔP.
Why tire pressure changes with temperature
The air inside a tire behaves roughly like an ideal gas in a container of fixed volume. When the temperature falls, the air molecules move more slowly and strike the tire walls less forcefully, so the pressure drops; when the temperature rises, the pressure rises. Gay-Lussac's law makes this relationship exact for an ideal gas: pressure is directly proportional to absolute temperature, measured in kelvin. That is why the calculator quietly converts your °C or °F input to kelvin behind the scenes.
A detail that many rule-of-thumb charts get wrong is the distinction between gauge and absolute pressure. Your gauge reads zero when the tire is at atmospheric pressure, but the air inside is still at ~14.7 psi absolute. The temperature acts on the absolute pressure, so the correct calculation must add atmospheric pressure first and subtract it again at the end. Doing this properly is what this calculator does — and it is also why the answer depends slightly on your altitude.
In practice, a typical passenger-car tire loses or gains roughly 1 psi for every 10 °F (about 5–6 °C) of temperature change. A car parked in a 20 °C garage and then left overnight at −10 °C can drop from 32 psi to about 27 psi — enough to trigger a TPMS low-pressure warning and to noticeably worsen handling, braking and fuel economy. The effect also works in reverse: pressure measured after a long drive, when the tires are warm, reads several psi higher than the "cold" pressure the manufacturer specifies.
Assumptions and practical tips
- Constant volume. The tire is assumed rigid. Real tires expand slightly under pressure, so measured changes are typically a few percent smaller than calculated.
- Dry air. Humid shop air can condense at low temperatures, slightly reducing the pressure drop predicted here. Nitrogen-filled tires follow the same law.
- Air temperature, not tire temperature. Enter the temperature the tire is soaking in. After driving, the tire carcass is warmer than the ambient air — if you measure pressure right after a trip, use the approximate warm-tire temperature as T₁.
- Always check pressures cold. Manufacturers specify cold inflation pressure (usually measured at ambient temperature after the car has been parked for a few hours). Adjust pressures in the morning before driving whenever possible.
- Adjust for the season, not the moment. In winter, inflate to the placard pressure at the coldest expected temperature rather than topping up to the placard value in a warm garage, or you will overinflate once the tire cools down outside.
- Altitude matters a little. At 1,500 m (5,000 ft) above sea level, atmospheric pressure is around 12.2 psi instead of 14.7 psi. The calculator handles this — just enter your local value.
Quick reference: 32 psi tire at sea level
The table below shows the expected pressure for a tire inflated to 32 psi (gauge) at 20 °C and 14.7 psi atmospheric pressure. Values for other starting pressures scale almost linearly.
| Temperature change | New temperature | ΔP (psi) | New pressure (psi) |
|---|---|---|---|
| −30 °C | −10 °C | −4.8 | 27.2 |
| −20 °C | 0 °C | −3.2 | 28.8 |
| −10 °C | 10 °C | −1.6 | 30.4 |
| +10 °C | 30 °C | +1.6 | 33.6 |
| +20 °C | 40 °C | +3.2 | 35.2 |
| +30 °C | 50 °C | +4.8 | 36.8 |
Correct tire pressure affects safety, tire wear and rolling resistance. If you are preparing for a trip, you may also find our Tire Size Comparison, Vehicle Payload and Road Trip Fuel Stops calculators useful for planning.
Frequently Asked Questions
How do I calculate tire pressure change by hand without a calculator?
Convert both temperatures to kelvin (add 273.15 to °C, or use \\(K = (°F - 32) \times \tfrac{5}{9} + 273.15\)). Add atmospheric pressure to your gauge reading to get absolute pressure, multiply by \\(T_2/T_1\), then subtract atmospheric pressure from the result. Example: 32 psi at 20 °C cooled to 0 °C gives \\((32+14.7) \times \tfrac{273.15}{293.15} - 14.7 \approx 28.8\) psi.
How much does tire pressure drop overnight in winter?
Expect roughly 1 psi per 10 °F (about 0.06 psi per °C) of cooling. A tire at 32 psi in a 68 °F garage can lose 6–7 psi sitting overnight at 0 °F — enough to trigger a TPMS warning light. Check and adjust pressures in the morning before driving, when tires are cold and at the outdoor temperature.
Why does my tire pressure light come on when it gets cold?
TPMS warning thresholds are usually set around 25 % below the placard pressure. Since pressure falls about 2 % for every 10 °F drop, a sudden cold snap or the first frost can push a borderline tire below the threshold overnight. The light often turns off after driving warms the tires — but you should still check and top up, because the air really is missing.
Should I use the temperature of the air or the temperature of the tire?
Use the temperature the tire has soaked in. A parked car's tires match ambient air within a few degrees. But after 20–30 minutes of driving, the tire carcass and the air inside can be 20–30 °F warmer than the outside air, which is why pressures read 2–4 psi higher when measured warm. Manufacturers specify cold pressure, measured after the car has sat for at least three hours.
Does tire pressure change with altitude?
Yes, slightly. Higher altitude means lower atmospheric pressure, which changes the gauge-to-absolute conversion. At 5,000 ft, atmospheric pressure is about 12.2 psi instead of 14.7 psi. For a typical 32 psi tire the difference in the calculated change is a few tenths of a psi — small, but the calculator accounts for it if you enter your local value. Note: driving up a mountain also changes tire temperature, which usually matters more.
Does nitrogen-filled tires' pressure change with temperature?
Nitrogen obeys the same gas laws as dry air, so the pressure change with temperature is essentially identical — this calculator works for both. Nitrogen's benefits are mainly its dryness (no moisture condensing or extra pressure from humidity) and slower leakage through the rubber. Marketing claims that nitrogen drastically reduces temperature sensitivity are exaggerated.
Is the 1 psi per 10 °F rule of thumb accurate?
It's a good approximation for typical passenger-car tires (28–36 psi at sea level). The exact change is proportional to absolute pressure, so higher-pressure tires change more — a truck tire at 80 psi gains or loses about 2 psi per 10 °F, while a spare at 60 psi changes about 1.5 psi. The exact Gay-Lussac calculation used here is always more precise than the rule of thumb.