How to use this calculator
- Choose the pitch value you know. Select module, diametral pitch or circular pitch.
- Enter the pitch value. Enter module or circular pitch in mm, or diametral pitch in 1/in.
- Enter tooth count. The tooth count is used to calculate pitch diameter.
- Read the equivalent pitch values. Read module, DP, circular pitch, pitch diameter and standard full-depth tooth proportions.
How it works
Gear pitch values are different ways to describe the same tooth size:
p = π · m DP = 25.4 / m
where p is circular pitch, m is module and
DP is diametral pitch. Once module and tooth count are known, pitch
diameter is d = m·z.
Worked example
Verified against the live calculator
Module 2 mm gives circular pitch
p = π × 2 = 6.28 mm and diametral pitch
DP = 25.4 / 2 = 12.7. With 20 teeth, pitch diameter is
d = 2 × 20 = 40 mm.
Frequently asked questions
What is gear pitch?
Gear pitch describes tooth size. Metric gears use module m, imperial gears use diametral pitch DP, and circular pitch p is the arc distance from one tooth to the next on the pitch circle.
How do module and diametral pitch convert?
They are reciprocals scaled by 25.4: module m = 25.4 / DP, and DP = 25.4 / m. A module 2 gear is about DP 12.7.
How do you calculate circular pitch?
Circular pitch is p = π·m. It is the distance along the pitch circle from one tooth to the same point on the next tooth.
How do you calculate pitch diameter from pitch?
For module gears, pitch diameter d = m·z where z is tooth count. For DP gears in inches, d = z / DP.
Do mating gears need the same pitch?
Yes. Mating spur gears must share the same module or diametral pitch and pressure angle. Tooth count can differ, but pitch system cannot.
Method & assumptions
- External spur gear pitch values; helical gears need normal/transverse pitch handling.
- Standard full-depth reference values are shown for addendum and whole depth.
- Pitch diameter is not the same as outside diameter; standard outside diameter is about d + 2m.