About Engine RPM & Speed Calculator
Solve for engine RPM or vehicle speed based on transmission gear ratio, differential final drive, and tire diameter. Ideal for checking highway cruising RPM in overdrive or selecting axle ratios.
Key Capabilities & Features
- Two-way solver: Calculate Engine RPM from speed, or calculate Speed from RPM
- Inputs for transmission gear ratio, differential final drive ratio, and tire diameter
- Identifies highway cruising engine RPM to optimize fuel economy in overdrive gears
- Outputs dual velocity readings in miles per hour (mph) and kilometers per hour (km/h)
How to Use Engine RPM & Speed Calculator
Choose Target Variable
Select whether to solve for Engine RPM or Vehicle Road Speed.
Input Gearing Parameters
Enter transmission gear ratio, final drive ratio, and tire diameter.
Input Speed or RPM
Enter desired highway speed or target engine operating RPM.
Review Results
See exact calculated RPM or road speed.
Privacy & In-Browser Execution Guarantee
100% client-side calculation. Your data never leaves your browser.
Frequently Asked Questions
What is the formula for RPM from vehicle speed?
RPM = (Speed in mph × Gear Ratio × Final Drive × 336) / Tire Diameter in inches.
What is an overdrive gear ratio?
An overdrive gear has a ratio less than 1.0 (e.g. 0.77:1), meaning the transmission output shaft rotates faster than the engine crankshaft, lowering RPM and saving fuel at highway speeds.