Enter your Vehicle Speed, Tire Diameter, Rear Gear Ratio, and Transmission Gear Ratio into the RPM Calculator to find your Engine RPM at any given speed — plus your Tire Revolutions per Mile and Final Drive Ratio as a bonus.
Engine RPM
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Tire Revolutions per Mile
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Final Drive Ratio
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Tire diameter can be calculated from tire size markings (e.g., 265/70R17) or measured directly. Add the wheel diameter to twice the sidewall height. Online tire calculators can help convert tire size to overall diameter.
Rear gear ratio is the ratio between ring gear teeth and pinion gear teeth in your differential. Common ratios range from 2.73:1 to 4.56:1. Check your vehicle's build sheet, differential tag, or count the teeth on both gears.
Use 1.0 for direct drive (usually 4th gear in manual transmissions), 0.7-0.8 for overdrive gears, and higher ratios for lower gears. Check your transmission specifications for exact ratios.
Knowing your RPM at cruising speed helps optimize fuel economy, select appropriate gear ratios, and ensure your engine operates within its power band. It's crucial for gear ratio changes and performance modifications.
This calculator provides theoretical RPM based on mechanical ratios. Actual RPM may vary slightly due to tire flex, slip, drivetrain losses, and manufacturing tolerances, but results are typically within 1-3% of actual values.
Yes, this calculator works for manual, automatic, and CVT transmissions. Simply input the gear ratio for the specific gear you're analyzing. For automatics, use the converter lock-up ratio when applicable.