Enter your ring & pinion ratio, tire height, vehicle speed, and transmission ratio to calculate your engine's RPM. The Transmission Calculator also lets you map up to 6 gear ratios to see the speed your vehicle reaches in each gear at a given engine RPM.
Calculated Engine RPM
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Speed in 1st Gear
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Speed in 2nd Gear
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Speed in 3rd Gear
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Speed in 4th Gear
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Speed in 5th Gear
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Speed in 6th Gear
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The formula is: RPM = (Speed × Axle Ratio × Transmission Ratio × 336) / Tire Height. The constant 336 accounts for unit conversions (minutes to hours and inches to miles). Higher axle or transmission ratios result in higher engine RPM at the same road speed.
A transmission gear ratio is the relationship between the rotational speed of the input (engine) shaft and the output (driveshaft) shaft within the gearbox. A ratio of 2.0 means the engine turns twice for every one turn of the output shaft, providing more torque but less speed.
The ring and pinion ratio is the number of ring gear teeth divided by the number of pinion gear teeth in your rear differential. A higher axle ratio (e.g. 4.10) gives more torque and acceleration, while a lower ratio (e.g. 2.73) improves fuel economy and top-end speed.
Tire height (overall diameter) can be calculated from the tire size printed on the sidewall. For example, a 265/75R16 tire has an approximate diameter of about 31.6 inches. You can use a dedicated tire height calculator or measure the tire directly from the ground to the top of the tread.
Gear ratios vary by transmission model. A common 6-speed manual might have ratios like: 1st – 2.97, 2nd – 2.07, 3rd – 1.43, 4th – 1.00, 5th – 0.84, 6th – 0.56, with a reverse of around 3.28. Overdrive gears (below 1.0) allow the driveshaft to spin faster than the engine for better highway fuel economy.
A numerically higher axle ratio means the engine must spin faster to maintain a given road speed, which typically reduces fuel economy at highway speeds. A lower axle ratio keeps engine RPM down on the highway, improving efficiency — but it can reduce off-the-line acceleration and towing capability.
An overdrive gear has a ratio below 1.0 (e.g. 0.72 or 0.84), meaning the transmission output shaft spins faster than the input shaft. This lowers engine RPM at highway speeds, reducing fuel consumption and engine wear. Most modern transmissions have at least one overdrive gear.
Yes. The formulas apply equally to manual and automatic transmissions. Simply enter the gear ratios from your specific transmission's specification sheet. For automatic transmissions, the converter slip ratio at stall is a separate consideration not included in this basic calculation.