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Everyday Life Calculators
RPM Calculator
Estimate engine RPM at a given road speed from the gear ratio and tire diameter.
Engine speed
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About the RPM Calculator
Engine RPM at a given road speed depends on the tire's rolling diameter and the vehicle's overall gear ratio (the transmission gear ratio multiplied by the final drive/differential ratio).
Formula: RPM = (Speed in mph × Overall Gear Ratio × 336) ÷ Tire Diameter (in). The constant 336 converts miles per hour and tire revolutions into RPM.
Useful for checking whether a gear or tire change will keep the engine in its efficient RPM range at highway speed.
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