Engine RPM Calculator

Use the calculator below to calculate your engine RPM.

Ring & Pinion Gear Ratio

Tire Diameter

incm

Speed

mphkm/h

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Results: Calculated Engine RPM

Automatic

 

RPM

Automatic in Overdrive

 

RPM

Manual < 5-Speed

 

RPM

Manual >= 5-Speed

 

RPM

Learn how we calculate this below

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By

Joe Sexton

Joe is the creator of Inch Calculator and has over 20 years of experience in engineering and construction. He holds several degrees and certifications.

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Sexton, J. (n.d.). Engine RPM Calculator. Inch Calculator. Retrieved June 30, 2026, from https://www.inchcalculator.com/engine-rpm-calculator/

How to Calculate Engine RPM

Engine RPM (revolutions per minute) is a measurement of how fast an engine’s crankshaft is rotating. Knowing engine RPM is useful when selecting tire sizes, choosing differential gear ratios, improving fuel economy, and evaluating vehicle performance.

You can use a formula to calculate engine RPM if you know the vehicle speed, tire diameter, ring and pinion (differential) gear ratio, and transmission gear ratio.

Engine RPM Formula

When using a 1:1 transmission gear ratio (such as direct drive), engine RPM can be calculated using the following formula:

RPM = speed × gear ratio × 336 / tire diameter

So, the engine’s RPM is equal to the speed in miles per hour times the ring and pinion gear ratio times 336, divided by the tire size in inches.