🚗 Tire Pressure Calculator
Calculate the correct tire pressure with temperature adjustment using Gay-Lussac's Law. Convert between PSI, bar, kPa, and atm. Includes recommended pressure by vehicle type, cold vs. hot pressure guidance, and TPMS threshold information.
Why Tire Pressure Matters
Proper tire pressure is critical for safety, fuel efficiency, and tire longevity. Underinflation increases rolling resistance (reducing fuel economy by up to 3%), causes uneven tread wear, and generates excess heat that can lead to blowouts. Overinflation reduces traction and causes center-tread wear.
According to NHTSA, tires with low pressure contribute to over 11,000 tire-related crashes annually on U.S. roads. Checking tire pressure monthly is one of the simplest and most effective vehicle maintenance tasks.
How Temperature Affects Tire Pressure
Air inside a tire behaves as a closed ideal gas, obeying Gay-Lussac's Law: absolute pressure is proportional to absolute temperature. For automotive tires, the practical rule of thumb is approximately 1 PSI change for every 10 °F (or ~1.24 kPa per 1 °C).
P₂ = P₁ × (T₂ + 459.67) / (T₁ + 459.67)
where P is gauge pressure (PSI) and T is temperature (°F, absolute)
A tire set to 35 PSI on a 70 °F summer afternoon will read about 31 PSI on a 30 °F winter morning — without any actual air loss. The air did not leak; it just got cold and contracted. This is why TPMS warnings often trigger on the first cold morning of fall.
Cold Pressure vs Hot Pressure
Tire pressure specifications on the door jamb are always "cold" pressure — meaning the tires have been parked and at ambient temperature for at least 3 hours, and the vehicle has not been driven more than a mile or so since.
- Cold pressure: The reference point — always set pressure cold.
- Hot pressure: 4–8 PSI higher than cold, due to heat buildup from driving.
- Never bleed pressure from a hot tire to reach the cold spec.
- If checking hot, set 2–4 PSI above cold spec, then recheck cold in the morning.
Recommended Pressure by Vehicle Type
Optimal tire pressure varies by vehicle type, weight, and load. Always check the manufacturer's recommendation in the door jamb or owner's manual. General ranges include:
- Compact Car: 28–33 PSI
- Sedan / Family Car: 30–35 PSI
- Performance Car: 32–36 PSI
- Crossover SUV: 35–40 PSI
- Full-Size SUV: 40–45 PSI
- Pickup Truck (Light): 35–45 PSI (increase for heavy loads/towing)
- Light Trailer: 50–65 PSI
- Donut Spare: 60 PSI
Why Use This Calculator?
- Temperature correction: Automatically adjusts pressure for current temperature using Gay-Lussac's Law.
- Unit conversion: Works with PSI, bar, kPa, and atm.
- Load adjustment: Accounts for heavy loads and towing.
- Step-by-step breakdown: See exactly how the calculation is performed.
- Free & private: No registration, no data storage — all calculations are done in your browser.
❓ Tire Pressure Calculator FAQ
What is the correct tire pressure for my car?
The correct pressure is on the door jamb sticker (driver's side) or in your owner's manual — not the tire sidewall. Most passenger cars need 28–36 PSI; SUVs and trucks typically need 35–45 PSI.
How much does temperature affect tire pressure?
Tire pressure changes by approximately 1 PSI for every 10 °F (or ~1.24 kPa per 1 °C) change in ambient temperature. A tire set to 35 PSI at 70 °F will read about 31 PSI at 30 °F.
Should I check tire pressure hot or cold?
Always check when tires are cold — parked for at least 3 hours and driven less than 1 mile. Hot tires read 4–8 PSI higher due to heat buildup from driving. Never bleed air from a hot tire to reach the cold spec.
What happens if I drive with low tire pressure?
Underinflation increases rolling resistance (reducing fuel economy by up to 3%), causes uneven tread wear, generates excess heat, and can lead to tire blowouts. It is a major safety hazard.
What is the rule of thumb for tire pressure and temperature?
Approximately 1 PSI per 10 °F (or ~1.24 kPa per 1 °C). For a tire in the low 30s PSI, this works out to about 1 PSI per 6 °C.
Does nitrogen affect tire pressure?
Nitrogen-filled tires lose pressure more slowly (nitrogen molecules are larger) and are less affected by temperature. However, the real-world benefit is small — regular air (78% nitrogen) works fine with monthly checks.
What PSI should my tires be in winter?
Set pressure to the cold placard spec in winter. Because pressure drops ~1 PSI per 10 °F, you may need to top off in fall and spring. Do not reduce pressure for winter driving.
How do I convert PSI to bar or kPa?
1 PSI = 0.0689 bar = 6.895 kPa. 1 bar = 14.504 PSI = 100 kPa. Use the conversion table in this calculator for quick reference.
What is the maximum tire pressure?
The maximum pressure is printed on the tire sidewall (e.g., "Max Press 44 PSI"). This is not the recommended pressure — it is the maximum safe pressure for the tire. Always use the vehicle placard for the recommended value.
Is this calculator free?
Yes, this calculator is completely free to use. No registration or personal data storage is required.