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Gear Ratio, Mechanical Advantage & Torque Multiplier Calculator

Calculate simple and compound gear train reduction ratios (GR), output shaft RPM speed reduction, mechanical torque multiplication (ft-lbs), and drive efficiency.

Motor pinion gear
Axle / load spur gear
e.g. Standard 4-pole AC induction motor = 1,750 RPM
Precision spur gears = ~95-98%, worm drive = ~60-80%

Calculation Results

Gear Reduction Ratio: 4.00 : 1 Reduction Mechanical Advantage: 4.00x
Output Shaft Speed: 437.5 RPM
Multiplied Output Torque: 17.1 ft-lbs (23.2 Nm) 3.8x torque boost (at 95% efficiency)
Output Mechanical Power: 1.42 Horsepower (1.06 kW)

About This Calculator

Calculate simple and compound gear train reduction ratios (GR), output shaft RPM speed reduction, mechanical torque multiplication (ft-lbs), and drive efficiency.

Frequently Asked Questions

How is gear ratio calculated?

The gear ratio (GR) is calculated by dividing the number of teeth on the driven gear (output) by the number of teeth on the driver gear (input): Gear Ratio = N_driven / N_driver.

What is the trade-off between speed and torque in gearing?

Gears obey the law of conservation of power: reducing speed increases torque by the exact same ratio (minus mechanical friction losses). A 4:1 gear reduction cuts output speed by 75% but quadruples output torque.

What effect does an idler gear have on the gear ratio?

An idler gear inserted between the driver and driven gear changes the direction of rotation, but has zero effect on the overall gear ratio.

How do you calculate horsepower from torque and RPM?

The mechanical horsepower formula is: Horsepower (HP) = [Torque (ft-lbs) x Speed (RPM)] / 5,252. Torque and horsepower curves always cross at exactly 5,252 RPM.