Find the reduction ratio teeth₂ / teeth₁ and the output speed rpm₂ = rpm₁ / ratio.
| Ratio | – |
| RPM out | – |
Use this calculator for two meshing gears (or toothed pulleys counted the same way). The ratio is driven teeth divided by driving teeth. A 12-tooth pinion driving a 36-tooth gear is a 3:1 reduction: the output turns at one third of the input speed and, ignoring losses, carries about three times the torque.
3000 rpm in with 12 and 36 teeth gives 1000 rpm out. Tooth counts must be at least 1. This is a kinematic ratio only: it does not include gearbox efficiency, backlash, or a multi-stage train.
Teeth in: Teeth on the driving gear.
Teeth out: Teeth on the driven gear.
RPM in: Input rotational speed.
Ratio: t₂ / t₁ (reduction if greater than 1).
RPM out: Input speed divided by the ratio.
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