Gear Ratio Calculator: Output RPM and Torque
Enter the teeth on the driving and driven gears, and the input speed and torque. You get the ratio, output rpm and output torque, for one or two gear stages.
- Nothing you type is stored
- Free
- No signup
Gear ratio
3 : 1
Reduction- Output speed
- 480 Input speed
- Output torque
- 30 N·m
One gear pair: the output turns the opposite way to the input.
Show working
- 60 ÷ 20 = 3
- 1,440 ÷ 3 = 480 rpm
How to use
- Enter teeth on the driver (input) and driven (output) gear.
- Tick two stages if there is a second gear pair, and enter its teeth.
- Enter input rpm and torque to see the output.
Good to know
Gear ratio = driven teeth ÷ driver teeth. For two stages, multiply the ratios. Output speed = input speed ÷ ratio; output torque = input torque × ratio × efficiency. A 20-tooth gear driving a 60-tooth gear is 3 : 1, cutting 1,440 rpm to 480 rpm and tripling torque.
Ratio above 1 is a reduction (slower, more torque); below 1 is an overdrive (faster, less torque). Each spur gear stage loses roughly 1–3%; worm gears can lose much more, so enter efficiency if you know it.
The same idea applies to chain sprockets (count teeth) and belt pulleys (use diameters; see the RPM calculator). Indian induction motors usually run near 1,440 rpm (4-pole) or 2,880 rpm (2-pole) at 50 Hz.
Questions
How do I calculate gear ratio?
Divide the teeth on the driven gear by the teeth on the driving gear.
What is the output speed of a 3 : 1 reduction at 1,440 rpm?
1,440 ÷ 3 = 480 rpm.
Does a reduction increase torque?
Yes, by the ratio (minus losses). 10 N·m through 3 : 1 gives about 30 N·m.
How do I handle an idler gear?
An idler between two gears does not change the ratio, only the direction.
Can I use it for bicycle gears?
Yes: chainring teeth as driver, rear sprocket as driven; ratio below 1 means the wheel turns faster than the pedals.