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Wheel Circumference Calculator

Work out wheel circumference instantly with clear inputs, formula shown and shareable results.

About Wheel Circumference Calculator

Geometric circumference is pi times diameter, but the rolling circumference is about 3% less because the tyre deflects under load. That rolling figure is what determines revolutions per kilometre and therefore speedometer and odometer calibration.

Formula

Rolling circumference

diameter = rim x 25.4 + 2 x width x aspect/100; rolling circumference approx pi x diameter x 0.97

Worked example

With the default values below, Wheel Circumference Calculator returns Rolling circumference of 2,010.33. Change any input above and every figure here is recalculated in your browser.

Inputs used

Tyre width
225 mm
Aspect ratio
45 %
Rim diameter
18 in
Road speed
100 km/h

Results

Rolling circumference
2,010.33 mm
Overall diameter
659.70 mm
Revolutions per kilometre
497 rev/km
Wheel RPM at that speed
829 rpm

Step by step

  1. 1Values used
  2. 2Rolling circumference
  3. 3Rolling circumference= 2,010.33 mm
  4. 4Overall diameter= 659.70 mm
  5. 5Revolutions per kilometre= 497 rev/km
  6. 6Wheel RPM at that speed= 829 rpm

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why is rolling circumference less than geometric?

The contact patch flattens, so the effective radius is slightly smaller than the free radius. Manufacturers publish measured rolling circumference for this reason.

Where is revolutions per kilometre used?

In speedometer calibration, ABS wheel-speed reference values and gearing calculations. It is stamped in tyre specification tables.

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