Engine RPM Calculator
SI
Imp
Imperial
Inputs
View results
Road speed
(v)
Vehicle road speed.
mph
Tire diameter
(D)
Rolling tire diameter. Use measured rolling diameter for precision.
in
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.
Results
Default result
Edit inputs
Engine speed
(n_e)
2,351
rpm
Pass
Also computed
Wheel speed
(n_w)
840.3
rpm
Overall ratio
2.797
Speed per 1000 rpm
27.65
mph
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.
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