# Base Circle

Base circle, abbreviated as BC, is a circle from where involute portion of tooth profile will be produced. The base circle of a gear is an important concept in gear geometry. It is a theoretical circle that is used as a reference in the design of involute gears. The base circle is defined as the circle from which the involute curve of the gear tooth is generated.

## Base Circle formula |
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\(\large{ BC = PD \; cos\left( PA\right) }\) | ||

Symbol |
English |
Metric |

\(\large{ BC }\) = base circle | \(\large{in}\) | \(\large{mm}\) |

\(\large{ PD }\) = pitch diameter | \(\large{in}\) | \(\large{mm}\) |

\(\large{ PA }\) = pressure angle | \(\large{deg}\) | \(\large{rad}\) |

Tags: Gear