Tire Size Calculator – Compare Stock vs New
Enter sizes like 225/45R17 or use the fields. Then compare diameter, revs/mile (or per km), ride-height change, and speedometer error.
You can also fill the fields below.
Example: 205/55R16, 195/65R15, 275/40R19
You can also fill the fields below.
Supports R or dash: 235/40-18, 255 35 19, etc.
Used for speedometer error
Results will appear here.
How the calculations work
Tire sizes are given as Width/Aspect R Rim, e.g., 225/45R17.
- Sidewall Height (mm) = Width × (Aspect ÷ 100)
- Rim Diameter (mm) = Rim(in) × 25.4
- Overall Diameter (mm) = 2 × Sidewall + Rim(mm)
- Circumference = π × Diameter
- Revs per mile = 63,360 ÷ Circumference(in)
- Revs per km = 1,000,000 ÷ Circumference(mm)
- Speedometer: Actual = Indicated × (New Diameter ÷ Stock Diameter)
- Ride height change = (New Diameter − Stock Diameter) ÷ 2
Note: This calculator compares tire sizes only. Wheel width, offset, brake and fender clearances, and load/speed ratings are not assessed.
Frequently Asked Questions
Which formats can I enter?
Try 225/45R17, 225/45-17, or 225 45 17. Width and aspect are metric; rim is inches.
What’s a safe diameter change?
Many guides suggest keeping overall diameter within ~3% of stock for speedometer accuracy and clearance. This is not a guarantee—always check clearances.
Why do revs per mile matter?
They relate to gearing and speedometer calibration. Fewer revs/mile typically means a larger diameter tire.
Is my data private?
Yes. Everything runs locally in your browser.