Tire Pressure Check Calculator Formula
Understand the math behind the tire pressure check calculator. Each variable explained with a worked example.
Formulas Used
Temperature-Adjusted PSI
temp_adjusted_psi = current_psi + temp_change_f / 10Fuel Economy Penalty
fuel_penalty_pct = max(psi_underinflation, 0) * 0.2PSI to Add
psi_to_add = max(recommended_psi - current_psi, 0)Variables
| Variable | Description | Default |
|---|---|---|
recommended_psi | Recommended Tire Pressure(psi) | 35 |
current_psi | Current Tire Pressure(psi) | 30 |
temp_change_f | Temperature Change(°F) | -20 |
psi_underinflation | Derived value= recommended_psi - current_psi | calculated |
How It Works
Tire Pressure and Temperature
Tire pressure changes by approximately 1 PSI for every 10°F change in temperature. Underinflated tires waste fuel and wear unevenly.
Rules of Thumb
Temperature Adjustment: ~1 PSI per 10°F change
Fuel Penalty: ~0.2% per 1 PSI below recommended
For every 1 PSI underinflated across all four tires, fuel economy drops about 0.2%. At 5 PSI under, that is 1% worse mileage and significantly accelerated tire wear.
Worked Example
Tires at 30 PSI (recommended 35) with a 20°F temperature drop.
- 01Temperature effect = -20 / 10 = -2 PSI
- 02Adjusted pressure = 30 + (-2) = 28 PSI
- 03Underinflation = 35 - 30 = 5 PSI
- 04Fuel penalty = 5 x 0.2% = 1.0%
Frequently Asked Questions
Where do I find the recommended tire pressure?
Check the driver's side door jamb sticker or your owner's manual. Do NOT use the pressure on the tire sidewall, which is the maximum, not the recommended pressure.
Should I check pressure when tires are cold?
Yes. Check before driving or after sitting for 3+ hours. Driving heats tires and increases pressure 2-4 PSI, which can mask underinflation.
How often should I check tire pressure?
At least monthly, and before long trips. Even new tires lose 1-2 PSI per month naturally through the rubber. Temperature swings in spring and fall cause significant changes.
Ready to run the numbers?
Open Tire Pressure Check Calculator