RPM to speed calculator (gear ratio)
See your speed at any rpm in any gear, or how a new final drive or tire size changes highway cruising speed.
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Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter engine speed, gear ratio, final drive ratio, tire width, aspect ratio and rim diameter.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Wheel rpm = engine rpm ÷ (gear ratio × final drive). Speed (km/h) = wheel rpm × tire circumference (m) × 60 ÷ 1000, with circumference = π × (rim × 25.4 + 2 × width × aspect ÷ 100).
Example
Inputs: Engine speed = 3,000 rpm, Gear ratio = 1, Final drive ratio = 3.7, Tire width = 205 mm, aspect ratio = 55 %. Result: Speed: 96.6 km/h; Speed in mph: 60 mph; Wheel speed: 810.8 rpm.
Limits and caveats
- It uses the nominal tire diameter; the loaded radius is a little smaller, so real speed is about 1% to 3% lower.
- Clutch or torque converter slip in automatics is not included.
Questions about this tool
Where do I find gear and final drive ratios?
In the owner's manual or the technical spec sheet of the car or transmission.
What does a higher final drive do?
A higher ratio such as 4.1 instead of 3.7 gives stronger acceleration but higher highway rpm and usually more fuel use.
Does it work for a CVT?
Only if you know the ratio at that moment, because a CVT ratio changes continuously.