What is a gear ratio?

Gear ratio is the ratio of the number of teeth on the driven gear to the number of teeth on the driver gear (Driven / Driver). A ratio greater than 1 means speed reduction and torque increase; less than 1 means speed increase and torque reduction.

How is output RPM calculated?

Output RPM = Input RPM / Gear Ratio. For example, if the driver has 20 teeth and the driven gear has 60 teeth, the ratio is 3:1, so a 900 RPM input produces 300 RPM output.

What does torque multiplier mean?

The torque multiplier equals the gear ratio. If the ratio is 3:1 the driven shaft produces 3 times the torque of the driver shaft (before accounting for friction losses, typically 95-99% efficiency for spur gears).

Does this account for efficiency losses?

No. The calculator assumes 100% mechanical efficiency. In practice, spur gear pairs lose about 1-3% per mesh. Multiply the torque result by your expected efficiency (e.g. 0.97) for a real-world estimate.

Can I use this for chain drives or belt drives?

Yes — the same ratio formula applies. Enter the number of teeth on the driving sprocket as "driver teeth" and the number on the driven sprocket as "driven teeth." Tooth counts replace pulley diameters in the ratio calculation.

What is a compound gear train?

A compound gear train has multiple gear pairs in series. Multiply the individual ratios of each pair together to get the overall ratio. This calculator handles one pair at a time — run it twice and multiply the results for a two-stage drive.

Gear Ratio Calculator

Name: Gear Ratio Calculator
Availability: InStock
Author: Nham Vu

Calculate gear ratio, output RPM, and torque multiplication from driver and driven gear teeth counts and input RPM.

Gear Parameters

Driver Gear Teeth (input shaft)

Driven Gear Teeth (output shaft)

Input RPM

Gear Ratio

3.00 : 1

Driven / Driver teeth

Output RPM

300.00

Speed on driven shaft

Torque Multiplier

3.00 x

Output torque vs. input torque

Drive Type

Speed Reduction — more torque, less speed

Summary

Calculate gear ratio, output RPM, and torque multiplication from driver and driven gear teeth counts and input RPM.

How it works

Enter the number of teeth on the driver (input) gear.
Enter the number of teeth on the driven (output) gear.
Enter the input shaft RPM.
Click Calculate to see the gear ratio, output RPM, and torque multiplier.
Adjust any value and recalculate instantly.

Use cases

Sizing gearboxes for electric motors and CNC machines.
Designing bicycle drivetrains and sprocket sets.
Calculating speed reductions in conveyor and winch systems.
Verifying torque output for automotive transmission stages.
Educational demonstrations of gear mechanics for students.
Checking existing gear trains before retrofitting motors.

Frequently Asked Questions

Last updated: 2026-05-23 · Reviewed by Nham Vu