About the Speedometer Error Calculator
How a tyre size change shifts your speedometer and odometer readings.
Also known as: speedo error calculator, odometer error, tire size speedometer, speedo correction.
How to use this calculator
- Enter original tyre diameter, new tyre diameter, indicated speed, odometer reading.
- The result updates instantly as you type — press Calculate (or Enter) at any time.
- Review the breakdown shown under the main result.
- Use Copy result or Share to save the answer or send a link with your inputs.
Formula
actual speed = indicated × new diameter ÷ old diameter
Worked example
Using the values pre-filled in the calculator above:
- Original tyre diameter = 632 mm
- New tyre diameter = 655 mm
- Indicated speed = 100 km/h
- Odometer reading = 1,000 km
the calculator returns:
- Actual speed: 103.64 km/h
- Error: 3.64 km/h
- Percentage error: 3.639%
- Actual distance for that odometer reading: 1,036.4 km