Gear Ratio
The ratio of input speed to output speed (i = n₁/n₂) — the central parameter of a gearbox that determines how much speed is reduced and torque is amplified.
Definition
The gear ratio (i) is the dimensionless ratio between the input and output quantity of a gearbox. In drive technology, it typically refers to the ratio of the input speed n₁ to the output speed n₂. For a speed reducer, i > 1: the output speed is lower than the input speed, but the output torque is higher. When i < 1, the gearbox is referred to as a step-up transmission.
The gear ratio can also be calculated from the tooth counts of the gear wheels: i = z₂/z₁ (output tooth count divided by input tooth count). For multi-stage gearboxes, the individual ratios multiply: i_total = i₁ × i₂ × i₃. Typical gearbox ratios range from 3:1 to 100:1; worm gearboxes can achieve single-stage ratios of up to approximately 100:1.
Practical Relevance
Choosing the correct gear ratio is critical for optimal motor utilization. Too small a ratio provides little torque amplification — the motor itself must deliver a high torque. Too large a ratio unnecessarily reduces the output speed. The TEA Gear Ratio Calculator lets you quickly determine the optimal ratio for your application.