# Pitch Diameter

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Pitch diameter, abbreviated as PD, is an imaginary diameter that is used in gear calculations.  It is the diameter of the pitch circle, which is an imaginary circle that represents the point where the teeth of two gears mesh together.  In other words, it is the diameter of the circle that defines the spacing of the gear teeth.  For other types of gears, such as helical or bevel gears, the calculation may involve different parameters, but the concept of pitch diameter is used in defining the size and characteristics of the gear.

### Pitch Diameter formula

$$PD \;=\; n \;/\; DP$$     (Pitch Diameter)

$$n \;=\; PD \; DP$$

$$DP \;=\; n \;/\; PD$$

Symbol English Metric
$$PD$$ = pitch diameter $$in$$ $$mm$$
$$n$$ = number of teeth on the diameter $$dimensionless$$
$$DP$$ = dimetrical pitch $$in$$ $$mm$$

### Pitch Diameter formula

$$PD \;=\; (n \; CP) \;/\; \pi$$     (Pitch Diameter)

$$n \;=\; (PD \; \pi) \;/\; CP$$

$$CP \;=\; (PD \; \pi) \;/\; n$$

Symbol English Metric
$$PD$$ = pitch diameter $$in$$ $$mm$$
$$n$$ = number of teeth on the diameter $$dimensionless$$
$$CP$$ = circular pitch $$in$$ $$mm$$
$$\pi$$ = Pi $$3.141 592 653 ...$$

Tags: Gear