Gear Ratio • RPM • Torque — Simple • Compound • Worm — Simulate • Explore • Practice • Quiz
A gear train is a mechanical system of two or more meshing gears used to transmit rotational motion and torque between shafts. The gear ratio is the fundamental parameter that determines how speed and torque are exchanged: it equals the number of teeth on the driven gear divided by the number of teeth on the driver gear (GR = NB / NA). When the driven gear has more teeth, the output speed decreases but torque increases proportionally — this is a speed reducer. Conversely, fewer teeth on the driven gear produce a speed multiplier with higher RPM but lower torque.
Simple gear trains consist of two meshing gears on separate shafts and provide a single-stage speed change. Compound gear trains use four or more gears arranged so that two gears share an intermediate shaft, allowing the overall gear ratio to be the product of individual ratios (GR = (NB/NA) × (ND/NC)). This enables very large or very small ratios in a compact arrangement. Worm gear drives use a screw-like worm meshing with a worm wheel and can achieve very high ratios (often 40:1 or more) in a single stage while also providing a self-locking feature that prevents back-driving.
The module (m) relates tooth size to gear diameter: m = d / N, where d is the pitch circle diameter and N is the number of teeth. The circular pitch is the arc distance between adjacent teeth along the pitch circle: p = pi × m. For two gears to mesh properly they must have the same module. The centre distance between two meshing spur gears equals (dA + dB) / 2. Output RPM is calculated as RPMin / GR, and output torque (assuming 100% efficiency) equals input torque multiplied by the gear ratio.
In Simulate mode, select a train type (Simple, Compound, or Worm), adjust teeth counts and input RPM, and watch animated gears rotate with correct meshing behaviour. Readout cards display gear ratio, output RPM, torque values, module, and pitch circle diameter in real time. Use presets like Speed Reducer 3:1, Clock Mechanism, or Worm Drive 40:1 to explore common configurations. Switch to Explore mode to study 12 gear concepts across Basics, Types, and Applications. Practice mode generates random calculation problems, and Quiz tests your knowledge with 5 questions per session.
This gear train calculator is designed for mechanical engineering students, machine design trainees, workshop instructors, automotive technicians, and anyone studying power transmission systems. It provides visual, interactive understanding of gear mechanics without requiring physical gear sets or laboratory equipment.