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Gear Calculators

Gear Diameter Calculator

Pitch, outside and root diameter of a spur gear from its module and tooth count.

Enter values

Results update as you type.

Result

Pitch diameter

80 mm

Outside diameter
84 mm
Root diameter
75 mm
Base diameter
75.175 mm
Circular pitch
6.2832 mm
Tooth height
4.5 mm
Diametral pitch
12.7 DP

About the Gear Diameter Calculator

Pitch, outside and root diameter of a spur gear from its module and tooth count.

Also known as: pitch diameter, gear size calculator, outside diameter gear, gear dimensions.

How to use this calculator

  1. Enter module, number of teeth, pressure angle.
  2. The result updates instantly as you type — press Calculate (or Enter) at any time.
  3. Review the breakdown shown under the main result.
  4. Use Copy result or Share to save the answer or send a link with your inputs.

Formula

pitch diameter = module × teeth · OD = d + 2m

Worked example

Using the values pre-filled in the calculator above:

  • Module = 2 mm
  • Number of teeth = 40
  • Pressure angle = 20 °

the calculator returns:

  • Pitch diameter: 80 mm
  • Outside diameter: 84 mm
  • Root diameter: 75 mm
  • Base diameter: 75.175 mm