To calculate the gear ratio of two gears, divide the number of teeth on the driven gear by the number of teeth on the driver gear. For a multistage gear system, multiply the gear ratio of each individual stage to get the gear ratio of the entire system.
Gears consist of toothed wheels that are attached to shafts. The teeth are interlocked in a manner such that as one wheel rotates, the adjacent wheel rotates in the opposite direction. The rotating wheels also differ in speed. When a number of gears are connected together, they form a system referred to as a gear train. Input is connected to the driver gear, while the output is connected to the driven gear.
If the connected wheels have varying sizes, the smaller gear rotates faster. The gear ratio, also known as the velocity ratio, is the difference between the speeds of the varying wheels. The ratio of the teeth between the wheels is inversely proportional to their speed. This means that the number of teeth on a wheel, say A, divided by the number of teeth on another wheel, say B, is equal to the number of revolutions made by wheel B divided by the number of revolutions made by wheel A.