Work out a gear ratio
Teeth in, ratio out — plus what the output shaft actually spins at.
Tools used in this guide
The job
A 12-tooth pinion driving a 60-tooth spur turns force into speed or the reverse: ratio 5:1 means five input turns for one output turn, and ~5× the torque. Add a second stage for compound reductions.
Teeth and RPM
Enter driver and driven tooth counts; optionally a second pair and an input RPM. The result is the overall ratio, the output speed, and the torque multiplier.
Worked example
12→60 then 14→42 with 3,000 RPM in: stages 5:1 and 3:1, overall 15:1, output 200 RPM, torque ≈ 15× (ideal, before friction).
Where it stops
Ideal meshing only — real trains lose a few percent per stage to friction, and direction of rotation flips each external stage. Belt ratios work the same arithmetic via pulley diameters.