What this converter does
This converter turns road speed in miles per hour into wheel RPM and back. Because a bigger wheel turns fewer times for the same speed, enter the wheel or tyre diameter. Type a speed and read the required RPM instantly.
Handy for choosing gearing or checking engine RPM at cruising speed. The default 25-inch diameter suits a car tyre; set your own for other wheels.
The units it covers
Rotational speed becomes road speed only once the wheel size is known — a bigger wheel covers more ground per turn, so diameter is required.
View all units & their values
| Unit | Symbol | Value | Mainly used |
|---|---|---|---|
| Rotational speed | rpm | N | Wheel revolutions per minute |
| Road speed | mph | v | Miles per hour |
| Wheel diameter | in | d | Tyre/wheel outside diameter |
The formula
Road speed is the wheel circumference times revolutions per minute, converted to miles per hour:
mph = π × d × rpm ÷ 1056Where:
- rpm = wheel revolutions per minute
- d = wheel diameter in inches
- 1056 = 63360 in/mile ÷ 60 min/hour
Worked example
Find the wheel RPM at 60 MPH on a 25-inch wheel.
rpm = mph × 1056 ÷ (π × d)60 × 1056 ÷ (π × 25) ≈ 806 rpmSo 60 mph on a 25-inch wheel needs about 806 wheel RPM.
The units in this example
Linear speed along the road. For a fixed wheel size, more speed needs more RPM.
- 60 mph ≈ 806 rpm (25 in)
- 37 mph ≈ 500 rpm (25 in)
- rpm = mph × 1056 ÷ (π d)
- diameter matters
Wheel revolutions per minute needed for that speed. Falls as wheel diameter rises.
- 806 rpm ≈ 60 mph (25 in)
- 500 rpm ≈ 37 mph (25 in)
- mph = π d × rpm ÷ 1056
- bigger wheel = fewer rpm