Engine RPM Calculator

Inputs

Road speed (v)

Vehicle road speed.

km/h

Tire diameter (D)

Rolling tire diameter. Use measured rolling diameter for precision.

Transmission ratio (G)

Selected gear ratio. Overdrive gears are less than 1.0.

Final drive ratio (F)

Axle or differential ratio.

Transfer ratio (T)

Transfer-case or auxiliary ratio. Use 1.0 if none.

Default result

Engine speed(n_e)

2,351rpm

Pass

Also computed

Wheel speed(n_w)840.3rpm

Overall ratio2.797

Speed per 1000 rpm44.5km/h

Vehicle speed at 1000 engine rpm.

Method notes 2 notes

Assumes no torque-converter slip, clutch slip, tire growth or rolling-radius change under load.
Use measured rolling diameter or tire manufacturer revs-per-mile data when calibrating speedometer or gearing.