Gear Ratio RPM Calculator — Output Speed from Gear Ratio
Enter input shaft RPM and gear ratio to find the output speed. The curve shows how output RPM drops as the ratio increases — a classic inverse relationship.
RPM
Input RPM divided by the gear ratio
- 1
Input shaft speed
1,500 - 2
Output RPM = Input ÷ Gear Ratio
1,500 ÷ 3 = 500
How does this calculator work?
Output RPM = Input RPM ÷ Gear Ratio. Ratios greater than 1 slow the output shaft; ratios less than 1 speed it up (overdrive). The torque multiplier equals the gear ratio — a 3:1 reduction triples output torque before friction losses.
Formula
How this is calculated
When two gears mesh, the fundamental speed relationship is N₁ × T₁ = N₂ × T₂, where N is rotational speed (RPM) and T is tooth count. Rearranging for output speed: Output RPM = Input RPM ÷ GR, where GR = T₂ ÷ T₁. A ratio of 3:1 delivers one-third of the input RPM at the output shaft; a ratio of 0.5:1 (overdrive) delivers double.
The XY plot shows this inverse (hyperbolic) curve for gear ratios 0.5 to 8 at the input RPM you entered. The highlighted dot marks your exact combination. This shape shows why small ratio changes near 1:1 cause larger absolute RPM shifts than the same ratio change at a high reduction.
Torque is inversely related to speed, so the output torque equals the input torque multiplied by the gear ratio (before friction losses). A 4:1 speed reduction quadruples available torque. Real gearboxes run at roughly 96–99% mechanical efficiency per gear pair, so the actual torque gain is slightly less than the theoretical multiplier.
Frequently asked questions
Output RPM = Input RPM ÷ Gear Ratio. Ratios above 1 reduce output speed; ratios below 1 (overdrive) increase it.
Torque scales inversely with speed. A 4:1 ratio reduces speed to one-quarter while multiplying torque by 4× (less friction losses). This trade-off is governed by conservation of power: P = Torque × angular velocity.
Overdrive is any ratio below 1:1, where the output shaft spins faster than the input. It reduces engine RPM at highway speeds, lowering fuel consumption — at the cost of reduced torque at the driven shaft.
Also known as
TG we-Calculate Editorial Team. (2026). Gear Ratio RPM Calculator — Output Speed from Gear Ratio [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/gear-ratio-rpm-calculator
TG we-Calculate Editorial Team. "Gear Ratio RPM Calculator — Output Speed from Gear Ratio." TG we-Calculate. 2026. https://we-calculate.com/calculator/gear-ratio-rpm-calculator.
TG we-Calculate Editorial Team, "Gear Ratio RPM Calculator — Output Speed from Gear Ratio," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/gear-ratio-rpm-calculator
@misc{wecalculate_gear_ratio_rpm_calculator, title = {Gear Ratio RPM Calculator — Output Speed from Gear Ratio}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/gear-ratio-rpm-calculator}}, year = {2026}, note = {TG we-Calculate} }
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