RPM to MPH
Calculator
Convert engine revolutions per minute into road speed using tire diameter and overall reduction. See MPH, KPH and wheel RPM together.
Your setup
Your results
CalculatedAt constant reduction, speed is proportional to engine RPM and tire diameter.
Assumes no slip and a circular tire with the entered diameter.
How the calculation works
Follow the formula and keep the input units consistent at every step.
wheel RPM = engine RPM / R; speed (m/s) = engine RPM × π × D(m) / (60 × R)- Combine all drivetrain reductions into R.
- Divide engine RPM by R.
- Multiply wheel RPM by circumference and convert minutes to seconds.
A Worked Example
3,600 rpm ÷ 5 = 720 wheel rpm. A 13-inch tire travels 1.03735 m per revolution, giving 12.4482 m/s or 27.85 MPH.
What Your Result Means
At constant reduction, speed is proportional to engine RPM and tire diameter.
Assumptions & Limitations
Assumes no slip and a circular tire with the entered diameter.
Common Mistakes
Enter total reduction, not only the axle ratio when primary or transmission gearing is present.
Questions about this calculation
Which values should I enter?
Combine all drivetrain reductions into R. Enter total reduction, not only the axle ratio when primary or transmission gearing is present.
How should I interpret the result’s precision?
Displayed results are rounded for readability. Intermediate calculations retain floating-point precision; extra displayed decimals do not improve your input accuracy.
Can I use metric units?
Yes. Select Metric above the calculator to convert your inputs. Results always state their units. Tire-size designations keep their conventional mm and inch units.
What are the main limitations?
Assumes no slip and a circular tire with the entered diameter.
Method, sources & relevant guides
Angular speed and tangential speed. Gear reductions follow tooth engagement and conservation of rotation count.
OpenStax — University Physics: rotation with constant angular accelerationMethod documentation updated October 18, 2026. Independent professional review has not been claimed. Read the calculation and review policy.