Gear Ratio Calculator
Calculate gear ratio, output speed and output torque for gearboxes, sprockets and pulleys.
gear ratio
speed
torque
gearbox
sprocket
pulley
reduction
motor
Input values
⚙
Enter values and click Calculate to see results here.
Formula
Ratio = N_driven / N_driving
Output RPM = Input RPM / Ratio
Output Torque = Input Torque × Ratio × η
Worked Example
Given: A motor at 1450 RPM drives a gearbox with ratio 10:1. Efficiency is 95%. Input torque is 5 Nm.
Step 1: Output RPM = 1450 / 10 = 145 RPM
Step 2: Output Torque = 5 × 10 × 0.95 = 47.5 Nm
Check: Power = 5 × 1450 × 2π/60 = 759 W. Output: 47.5 × 145 × 2π/60 = 721 W. Loss = 38 W (5%).
Engineering Notes
- Efficiency: Single-stage gears: 95-98%. Multi-stage: 90-95%. Worm gears: 50-85%. Always account for losses.
- Torque rating: The gearbox output torque rating must exceed the calculated output torque. Apply a service factor of 1.25-1.5 for shock loads.
- Motor sizing: Power (kW) = Torque (Nm) × RPM / 9549. This remains constant through the gearbox (minus losses).
- Backlash: Precision applications need low-backlash gearboxes (< 1 arcmin). Standard gearboxes have 5-15 arcmin backlash.
References
- AGMA 2001 — Fundamental Rating Factors