Calculators
Tire Size Calculator
Find a tire's diameter and circumference.
FreeNo sign-upWorks in your browser
Enter details
Result
Overall diameter
24.97 in
634 mm
Circumference
78.45 in
Revolutions per mile
808
About the Tire Size Calculator
Enter a tire's section width, aspect ratio, and rim diameter (like 225/45R17) and the calculator returns the overall diameter, circumference, and revolutions per mile. Use it to compare tire sizes and check how a new size affects your speedometer.
How to use the Tire Size Calculator
- 1Enter your section width, aspect ratio, and rim diameter.
- 2Read the result instantly — it recalculates as you type.
- 3Adjust the numbers to model different scenarios.
Frequently asked questions
How do I read a tire size?
225/45R17 means 225 mm wide, sidewall 45% of that height, on a 17-inch rim. This tool converts it to overall diameter.
Does tire size affect my speedometer?
Yes — a larger overall diameter makes your speedometer read low, and a smaller one reads high. Compare diameters to see the effect.