Free Tire Size Calculator
Compare tire sizes and speedometer error.
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About the Tire Size Calculator
Free tire size calculator. Enter a tire size like 225/45R17 to get overall diameter, sidewall height, circumference and revolutions per mile — and compare two sizes to find the speedometer difference.
How it works
- 1
Enter a tire size
Width, aspect ratio and wheel diameter.
- 2
Add a second size
Optional — to compare against your current tire.
- 3
See the results
Diameter, circumference and speedo error appear instantly.
Frequently asked questions
In 225/45R17, 225 is the width in millimetres, 45 is the aspect ratio (sidewall as a percent of width) and 17 is the wheel diameter in inches.
Yes. A larger overall diameter makes your speedometer read low. Compare two sizes here to see the exact percentage difference.