RPM to Speed Calculator
Works out road speed from engine RPM, gearing and tyre size — and the reverse, since speed per 1,000 rpm scales linearly. The table shows what each gear gives at the revs you entered.
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The formula
wheel rpm = engine rpm ÷ (gear ratio × final drive) speed = wheel rpm × tyre circumference × 60
Road speed is entirely determined by three things: how fast the engine turns, how much the drivetrain divides that down, and how far the tyre travels per revolution. Change any one and the speed changes proportionally.
What to watch out for
Three things set the answer, and only three:
- Tyre circumference. Distance covered per wheel revolution. A 3% larger tyre is 3% more speed at the same revs.
- Overall ratio. Gearbox × final drive. This divides engine speed down to wheel speed.
- Engine speed. Everything scales linearly with it, which is why "speed per 1,000 rpm" is a useful constant for each gear.
The gear table uses representative ratios rather than any specific car — swap in your own ratios one at a time using the gear field if you need exact figures.
Frequently Asked Questions
How do I calculate speed from RPM?
Divide engine RPM by the overall ratio to get wheel RPM, multiply by the tyre circumference, then convert to your speed unit. This calculator does all three steps.
What RPM should I be at on the motorway?
Most modern cars sit at 2,000–2,500 rpm at 70 mph in top gear. The speed-per-1,000-rpm figure tells you exactly where yours lands.
How does tyre size change my cruising revs?
Proportionally. A 3% taller tyre drops revs about 3% at the same road speed — roughly 75 rpm off 2,500.
Why is the gear table approximate?
It uses representative ratios for a typical gearbox, not your car's. Use it for the shape of the spread; enter your own ratio in the gear field for an exact figure.