Calculate how your tire pressure will change when the temperature changes, using the physics of gas pressure (Gay-Lussac's Law) — know before your TPMS light does.
📂 Automotive & TransportationEverything runs locally in your browser — no sign-up required, and no data is ever sent anywhere.
This tool estimates how much your tire pressure will rise or fall when the outside temperature changes, using the same physics that governs any sealed gas: pressure is proportional to absolute temperature when volume stays constant (Gay-Lussac's Law). Because a tire is essentially a fixed-volume container of compressed air, cooling that air makes its molecules move slower and push less forcefully on the tire's inner wall, lowering pressure — while warming it has the opposite effect. Enter your current tire pressure and the unit it's measured in (PSI, kPa, or bar), your current temperature, and the temperature you want to check against, and the calculator converts everything to absolute pressure and absolute temperature, applies the exact proportional relationship, and converts the result back to your chosen pressure unit. This is the same effect behind the well-known "1 psi per 10°F" rule of thumb that many drivers have heard, and it's also the most common reason a car's tire pressure warning light turns on during the first genuinely cold morning of the season — nothing is actually leaking, the air inside the tire has simply contracted with the drop in temperature.
Every autumn and winter, service departments see a predictable spike in customers convinced they suddenly have a slow leak, right around the first cold snap of the season. In the overwhelming majority of these cases, nothing is wrong with the tire at all — the air inside has simply contracted as the temperature dropped, exactly as basic gas physics predicts, and the modern tire pressure monitoring system (TPMS) required on most cars is simply doing its job by flagging the drop.
The underlying relationship is Gay-Lussac's Law, one of the classical gas laws: for a fixed amount of gas held at constant volume, pressure is directly proportional to absolute temperature. A tire's internal volume barely changes as temperature shifts (the rubber and wheel are essentially rigid compared to the air inside), which makes a tire a near-perfect real-world example of this law in action. The key detail most casual explanations skip is that the law works on absolute temperature and absolute pressure — not the gauge pressure your tire gauge shows you, and not Fahrenheit or Celsius directly, but temperature measured from absolute zero (Kelvin or Rankine) and pressure measured from a true vacuum (adding roughly 14.7 psi of atmospheric pressure to whatever your gauge reads).
This is exactly why the popular "1 psi per 10°F" rule of thumb is a useful approximation but not a precise law: it happens to work out reasonably well specifically in the pressure range most passenger car tires use (roughly 30-35 psi) and for everyday ambient temperature ranges, but the true relationship is a ratio of absolute temperatures, not a fixed slope. At different starting pressures, in extreme temperature swings, or when you want a genuinely precise number rather than a rough rule, computing the actual proportional relationship — as this calculator does — gives a more accurate answer than the shorthand rule.
It's worth being clear about the calculator's scope: it models the effect of ambient (outside air) temperature only, assuming the tire starts in a stable, "cold" condition — meaning it hasn't been driven on recently. Actually driving a car heats the tires through flex in the rubber and friction with the road surface, which can raise pressure by several additional psi within just a few minutes of driving, completely separate from any ambient temperature effect. This is exactly why tire manufacturers and vehicle manuals specify checking and setting pressure when tires are cold (ideally before driving, or after the car has been parked for at least a few hours) — checking a warm tire and "correcting" it down to the recommended cold-pressure number will actually leave the tire underinflated once it cools back down.
None of this means temperature-driven pressure changes should be chased with constant manual adjustments. The standard advice from vehicle manufacturers remains simple: set tire pressure to the recommended cold-pressure figure (found on the driver's door jamb sticker, not the number printed on the tire's own sidewall, which is a maximum rating rather than a recommendation), check it periodically — especially at the start of a new season — and top it up as needed. Understanding why the number moves with the weather, rather than reflexively worrying about a leak every time a warning light appears, is really what a tool like this is for.
Tire pressure comes from air molecules bouncing off the inside of the tire; as temperature rises, those molecules move faster and hit the tire wall harder and more often, raising pressure, and as temperature falls, the opposite happens and pressure drops — this is a direct consequence of the physical gas law relating pressure and absolute temperature at constant volume.
It's a reasonable approximation for typical passenger car tire pressures (around 30-35 psi) and everyday temperature swings, but it's not exact — the real relationship depends on the ratio of absolute temperatures (not a fixed psi-per-degree slope), which is what this calculator computes directly rather than relying on the rule of thumb.
No — set your tires to your vehicle manufacturer's recommended cold pressure (found on the door jamb sticker) when they're cold, and let it fluctuate naturally with the weather. This calculator is meant to help you understand and anticipate those fluctuations, not to prompt you to constantly re-adjust pressure.
No. It models only the effect of ambient (outside air) temperature change on a tire in a stable, "cold" state. Driving generates additional heat from tire flex and road friction, which can temporarily raise pressure by several more psi on top of the ambient-temperature effect modeled here — always check pressure when tires are cold for an accurate reading.
A drop of roughly 1 psi per 10°F (about 6°C) is completely normal and is often exactly what triggers a modern car's TPMS (tire pressure monitoring system) warning light on a cold morning. Check your actual tire pressure with a gauge and inflate to your vehicle's manufacturer-recommended cold pressure if it's below spec.