Gearbox ratio & output speed calculator
Work out what a gearbox does to motor speed and torque: enter motor RPM, ratio and efficiency, and read output speed and the torque multiplication.
Gearbox output speed & torque
Gearbox ratio
Formulas: n_out = n_motor / i and T_out = T_motor × i × η. Gearboxes reduce speed and multiply torque by the same factor (minus losses); service factor for shock loads is typically 1.5–2.0× nominal.
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Frequently asked questions
How do I calculate the output speed and torque of a gearbox?
Output speed is n_out = n_motor / i, and output torque is T_out = T_motor × i × η. A 1450 RPM motor through a 20:1 box with 95 % efficiency delivers 72.5 RPM at the output while multiplying torque by about 19×.
How do I find the gearbox ratio for a target output speed?
Use the reverse mode: the required ratio is the motor speed divided by the target output speed. The calculator then finds the nearest standard ratio from its list — 5, 7.5, 10, 15, 20, 25, 30, 40, 50, 60, 80 and 100.
Does the torque ratio equal the gearbox ratio?
Not exactly — torque is multiplied by ratio × efficiency, since gearbox losses reduce the ideal torque multiplication. The calculator shows both the raw ratio and the effective torque ratio, and for shock loads apply a service factor of typically 1.5–2.0× nominal.
AO Ctrl provides this tool for reference only.