RPM to Speed Gear Ratio Calculator
Vehicle speed from engine RPM, gear ratio and tire size.
Enter your values
ⓘ Live results
Results
- Vehicle speed
- 64.6 mph
- Wheel RPM
- 804.3
- Tire circumference
- 84.8 in
- Combined ratio
- 3.73
Quick answer
Vehicle speed is derived from engine RPM divided by the combined gear ratio, then converted using tire circumference.
speed (mph) = (RPM x tire diameter x pi x 60) / (gear ratio x final drive x 63360)
How to use the RPM to Speed Gear Ratio Calculator
- 1Enter engine RPM, the current gear ratio and final drive (axle) ratio.
- 2Enter the tire's overall diameter.
- 3The result converts engine speed into road speed using tire circumference.
Worked example
Using the values the calculator loads with:
Inputs
- Engine RPM3000 rpm
- Transmission gear ratio1.0
- Final drive ratio3.73
- Tire diameter27 in
Results
- Vehicle speed64.6 mph
- Wheel RPM804.3
- Tire circumference84.8 in
- Combined ratio3.73
Frequently asked questions
Where do I find gear ratios?
Check your vehicle's service manual or a drivetrain specification sheet for each gear and the final drive ratio.
Why does tire size matter here?
A larger tire covers more ground per wheel revolution, increasing road speed for the same RPM.
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.