Gear ratio and output speed
No slip and no efficiency loss.
Method
Worked case: 1,450 rpm, 20 driving 60, is a ratio of 3 and 483 rpm out.
Logic: how this figure is built.
How to read a gear ratio
This page answers two questions: how many times the driving gear turns for one turn of the driven gear, and what the output speed is if the input speed is known. It is a kinematic ratio. It is not a torque rating and not a gearbox selection.
Ratio is driven teeth divided by driving teeth. Output speed is input speed divided by that ratio. A 20-tooth driver and a 60-tooth driven gear are a ratio of 3. At 1,450 rpm in, the output is 483 rpm. The direction reverses for an external mesh. The page does not change the sign.
Teeth must be integers that can mesh. A ratio typed as 3.2 is not a tooth pair. Speed is the shaft speed at the mesh you named, not the motor nameplate if a belt sits in between. A compound train needs each mesh in turn. This page is one mesh.
Use it when a model or a sketch has a pinion and a wheel and you want the speed at the next shaft before anyone talks about power. Power is conserved only if you ignore loss. A real mesh loses some power, so output torque is not simply input torque times the ratio. That loss is not calculated here.
- Related: shaft power
- mechanical guide
Last checked 3 October 2026. See the disclaimer.