Gear Ratio Explained: Speed, Torque & How to Calculate It
Gear ratio is the heart of every drivetrain. It sets how output speed and torque relate to the input — the classic trade where slower means stronger.
Learn to read a ratio, compute it from tooth counts, and apply it to conveyor and machine design.
The formula
Ratio i = Z₂ ÷ Z₁, the driven teeth divided by the driver teeth. Output torque rises by i; output speed falls by i.
Worked example
A 20-tooth pinion driving a 60-tooth gear gives i = 60/20 = 3:1 — output runs at one-third speed with three times the torque.
Reduction vs overdrive
Ratios above 1:1 are reductions (slower, stronger). Below 1:1 is overdrive (faster, weaker).
Related calculators
Frequently asked questions
What is a reduction ratio?
Any ratio greater than 1:1 — the output is slower and delivers higher torque.
Does ratio change power?
Ideally no; gears trade speed for torque at constant power, minus small losses.
This guide is for educational purposes. Always verify against the relevant standard before final design.