Gear Ratio Speed Calculator
How fast are you going at a given RPM in a given gear?
Your numbers
Your results
Speed (mph)
Speed (mph)
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Speed (km/h)
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Wheel speed (RPM)
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Gear Ratio Speed Calculator by TheCalcTools
How the Gear Ratio Speed Calculator works
Enter engine RPM, the gear ratio you are in and the axle (final drive) ratio.
Wheel RPM is engine RPM divided by both ratios.
Speed is wheel RPM times tire circumference.
The formula
Wheel RPM = engine RPM ÷ (gear × final drive)Speed = wheel RPM × π × tire diameter
Worked example
Using the default values shown in the calculator:
| Engine speed (RPM) | 3000 |
|---|---|
| Transmission gear ratio | 1 |
| Final drive ratio | 3.73 |
| Tire diameter (in) | 27 |
- Wheel speed = 3,000 ÷ (1 × 3.73) = 804 RPM.
- With 27 in tires that is 64.6 mph (104.0 km/h).
Result:
| Speed (mph) | 64.6 |
|---|---|
| Speed (km/h) | 104.0 |
| Wheel speed (RPM) | 804 |
Frequently asked questions
Where do I find my gear ratios?
In the vehicle’s specification sheet or manual. Many manufacturers publish them online.
Why does a bigger tire raise speed?
A larger diameter covers more ground per revolution, so the same RPM gives a higher speed.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.