RPM to Speed Calculator
Vehicle speed from engine RPM.
Enter your values
ⓘ Live results
Results
- Speed
- 43.2 mph
- Speed in km/h
- 69.6
- Wheel RPM
- 570
- Tyre circumference
- 80.1 in
Quick answer
Road speed comes from wheel RPM after gearing, multiplied by tyre circumference.
Speed = RPM ÷ (gear × diff) × circumference
How to use the RPM to Speed Calculator
- 1Enter engine RPM and the gear ratio in use.
- 2Enter the final drive ratio.
- 3Enter tyre diameter in inches.
Worked example
Using the values the calculator loads with:
Inputs
- Engine RPM3000
- Gear ratio1.35
- Final drive ratio3.9
- Tyre diameter25.5 in
Results
- Speed43.2 mph
- Speed in km/h69.6
- Wheel RPM570
- Tyre circumference80.1 in
Frequently asked questions
Where do I find tyre diameter?
Calculate it from the sidewall code or measure it loaded.
Why is my speedo different?
Speedometers usually read 2–5% optimistic by design.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.