Engine RPM Calculator

Enter your axle gear ratio, tire diameter, vehicle speed, and transmission gear ratio in the blue fields and click the calculate button to find your engine RPM.

Axle Gear Ratio: : 1
Tire Diameter: Inches
Vehicle Speed: MPH
Transmission Ratio: : 1

Engine Speed: RPM

(See table below for common transmission ratios or use 1.00 for overdrive.)




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Axle Parts


Engine RPM Calculation Basics

Engine RPM, or the speed at which the engine turns, can be calculated at any speed given the vehicle's tire size, axle ratio, and final transmission gear ratio. This calculation is used to match oversize tires with new ring and pinion gears to obtain the desired engine RPM at highway speed.

[ (Axle Ratio x Vehicle Speed x Transmission Ratio x 336.13) / Tire Diameter ] = [ (3.73 x 65 x 1.00 x 336.13) / 31 ] = [ 2628 ]

Note: 336.13 is used to convert the result to RPM = [63360 inches per mile / (60 minutes per hour x Pi.)]



Popular Transmission Ratios

Transmission1st Gear2nd Gear3rd Gear4th Gear

Chrysler TF-727 2.45:1 1.45:1 1.00:1
Chrysler TF-904 2.45:1 1.45:1 1.00:1
Chrysler A-500 / 42RH 2.74:1 1.54:1 1.00:1 0.69:1
Chrysler A-518 / 618 / 47RH 2.45:1 1.45:1 1.00:1 0.69:1

Ford C4 2.46:1 1.46:1 1.00:1
Ford C6 2.46:1 1.46:1 1.00:1
Ford AOD 2.40:1 1.47:1 1.00:1 0.67:1
Ford AODE-W / 4R70W 2.84:1 1.55:1 1.00:1 0.70:1

GM Powerglide (Small Block) 1.76:1 1.00:1
GM Powerglide (Big Block) 1.82:1 1.00:1
GM 200-4R 2.78:1 1.57:1 1.00:1 0.67:1
GM TH350 / Turbo 350 2.52:1 1.52:1 1.00:1
GM TH400 / Turbo 400 2.48:1 1.48:1 1.00:1
GM 700R4 / 4L60E 3.06:1 1.63:1 1.00:1 0.70:1
GM 4L80E / 4L85E 2.48:1 1.48:1 1.00:1 0.75:1




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