Calculator
RPM at Speed Calculator
Work out engine rpm at any road speed — such as 70 mph or 130 km/h on the motorway — from the gear ratio, final drive and tyre size.
At 70 mph the engine turns 1,900 rpm in this gear.
Engine speed across the speed range
| mph | rpm |
|---|---|
| 30 | 814 |
| 40 | 1,085 |
| 50 | 1,357 |
| 60 | 1,628 |
| 70 | 1,900 |
| 80 | 2,171 |
| 90 | 2,442 |
| 100 | 2,714 |
Cruising rpm, gearing and fuel use
The wheels turn at speed ÷ tyre circumference; the gearbox and final drive multiply that up to engine speed. Tall top gears (ratios well under 1.0, such as 0.64 in an eight-speed automatic) keep the engine near 2,000 rpm at motorway speed, which is quieter and saves fuel. Short gearing makes a car feel lively but busier on a long drive.
Formulas
- rpm = speed (km/h) ÷ (tyre circumference (km) × 60) × gear ratio × final drive
An automatic with an open torque converter turns a little faster. For road speed from rpm, use the Gear Speed Calculator
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