Gear ratio calculator

Work out engine speed at any road speed from the gear ratio, the final drive and the tire size, with the overall drive ratio and revolutions per mile alongside.

One page, no account

Engine speed at road speed

Enter the tire, the gear you are in and the final drive. The arithmetic is stated on the how-it-works page, so you can check it by hand.

The tire decides how far one wheel revolution takes you, so it changes the answer as much as the axle does.

The ratio of the gear you are in. Top gear on most modern autos is below 1.

The differential ratio. 3.73 and 4.10 are the usual swap candidates.

The speed you want the engine figure for.

The answer

The fields already hold a worked example. Press Work out the engine speed and the answer appears here — computed in this browser, with every assumption it made listed underneath.

The arithmetic behind this page is written out on how this site works, so you can check it by hand.