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.)




NEW! - Need help with this calculator? Check out the new comments section below!


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 Gear5th Gear6th Gear

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
Chrysler TorqueFlite 727 2.45:1 1.45:1 1.00:1
Chrysler TorqueFlite 904 2.45:1 1.45:1 1.00:1
Chrysler TorqueFlite 999 2.74:1 1.55:1 1.00:1

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
Ford 4R100 2.71:1 1.54:1 1.00:1 0.71:1
Ford 5R150 TorqShift 3.11:1 2.22:1 1.55:1 1.00:1 0.71:1
Ford NP435(E) 6.68:1 3.34:1 1.74:1 1.00:1
Ford NP435(L) 6.68:1 3.34:1 1.66:1 1.00:1
Ford T18 6.32:1 3.09:1 1.69:1 1.00:1
Ford T19 4.02:1 2.41:1 1.41:1 1.00:1
Ford T19 (HD) 6.32:1 3.09:1 1.68:1 1.00:1
Ford T19 (Special) 5.11:1 3.03:1 1.79:1 1.00:1
Ford ZF 5.72:1 2.94:1 1.61:1 1.00:1 0.76:1

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 / 4L60 3.06:1 1.63:1 1.00:1 0.70:1
GM 4L60E / 4L65E 3.06:1 1.63:1 1.00:1 0.69:1
GM 4L80 / 4L85 2.48:1 1.48:1 1.00:1 0.75:1
GM 6L80 4.02:1 2.36:1 1.53:1 1.15:1 0.85:1 0.67:1
GM NP435(A) 4.56:1 2.28:1 1.31:1 1.00:1
GM NP435(D) 4.90:1 2.29:1 1.19:1 1.00:1
GM NV4500 (93-94) 6.34:1 3.44:1 1.71:1 1.00:1 0.73:1
GM NV4500 (95+) 5.61:1 3.04:1 1.67:1 1.00:1 0.74:1
GM Powerglide (Small Block) 1.76:1 1.00:1
GM Powerglide (Big Block) 1.82:1 1.00:1
GM SM420 7.00:1 3.60:1 1.70:1 1.00:1
GM SM465 6.55:1 3.58:1 1.57:1 1.00:1

Jeep AW4 2.80:1 1.53:1 1.00:1 0.75:1
Jeep AX15 3.92:1 2.33:1 1.44:1 1.00:1 0.85:1
Jeep AX4 3.83:1 2.33:1 1.44:1 1.00:1
Jeep AX5 3.83:1 2.33:1 1.44:1 1.00:1 0.79:1
Jeep BA10/5 3.39:1 2.33:1 1.44:1 1.00:1 0.79:1
Jeep NSG370 4.46:1 2.61:1 1.72:1 1.25:1 1.00:1 0.84:1
Jeep NV3550 4.01:1 2.33:1 1.39:1 1.00:1 0.78:1
Jeep SR4 (4 Cyl.) 4.07:1 2.39:1 1.49:1 1.00:1
Jeep SR4 (6 Cyl.) 3.50:1 2.21:1 1.43:1 1.00:1
Jeep T176 3.52:1 2.27:1 1.46:1 0.75:1
Jeep T177 3.82:1 2.29:1 1.46:1 0.75:1
Jeep T178 3.00:1 2.08:1 1.47:1 0.75:1
Jeep T18 (72-75) 6.32:1 3.09:1 1.69:1 1.00:1
Jeep T18 (76-79) 4.02:1 2.41:1 1.41:1 1.00:1
Jeep T18 / T19 6.32:1 3.09:1 1.69:1 1.00:1
Jeep T4 4.03:1 2.37:1 1.50:1 1.00:1
Jeep T5 4.03:1 2.37:1 1.50:1 1.00:1
Jeep T98 6.40:1 3.09:1 1.69:1 1.00:1
Jeep 42RLE 2.84:1 1.57:1 1.00:1 0.69:1
Jeep 45RFE 3.00:1 1.67/1.5:1 1.00:1 0.75:1
Jeep 5-45RFE 3.00:1 1.67/1.5:1 1.00:1 0.75:1 0.67:1








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