# Simple gear train with two gears (gear ratio in terms of radii of the gears and number of teeth)

## Description

The gear ratio of a gear train, also known as its speed ratio, is the ratio of the angular velocity of the input gear to the angular velocity of the output gear. The gear ratio can be calculated directly from the numbers of teeth on the gears in the gear train. The simplest example of a gear train has two gears. The “input gear” (a.k.a. the drive gear) transmits power to the “output gear” (a.k.a. the driven gear). The number of teeth on a gear is proportional to the radius of its pitch circle.

Related formulas## Variables

N_{A} | The number of teeth on the input gear (dimensionless) |

N_{B} | The number of teeth on the output gear (dimensionless) |

r_{A} | The radius of the input gear (m) |

r_{B} | The radius of the output gear (m) |