Calculate your result
Enter your figures below. Values stay in your browser.
How to use Tyre Size Calculator
- Enter your figures in the units shown beside each field. Keep monetary inputs in the same currency; money results are currently displayed in USD.
- Select the unit standard where the form offers a choice, then choose Calculate.
- Read the breakdown and compare the worked example below. Change one assumption to see its effect.
Formula used
Sidewall = width × aspect ratio/100. Diameter in mm = rim inches × 25.4 + 2 × sidewall. Circumference = π × diameter.
Worked example
225/45R17 gives a 101.25 mm sidewall, 634.30 mm nominal diameter and 1,992.71 mm circumference.
What the result means
Nominal geometry does not establish safe fitment. Check approved sizes, load and speed ratings, wheel compatibility and clearance.
Check your result
Results retain calculation precision internally and round for display. Keep the input values with the result so you can reproduce it. Use Reset to restore the example inputs, or Copy result to copy the displayed answer.
If the result does not agree with your own calculation, report the page, inputs and expected answer. See our methodology and reference sources for the standards used.
Related tools
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Tyre Circumference Calculator
Tyre Circumference Calculator turns width, profile and rim diameter into a result you can check against the figures from your car, route or workshop note.
Tyre Speed Difference Calculator
Use Tyre Speed Difference Calculator when a dashboard, advert or workshop note gives you two complete tyre sizes and their nominal difference in a different unit or format.
Formula, worked example and limitations updated September 10, 2026.