Module is millimetres per tooth
The module is the pitch diameter divided by the number of teeth; a standard gear’s outside diameter is the module times the teeth plus two.
Reference tool — not a selection
Find the module of a gear before it goes in an RFQ.
Gear module
Teeth and outside diameter.
Enter the number of teeth and the outside diameter. Below the examples, the module or DP of an offered gear can be checked: whether the two mesh. The gear and the RFQ line update with every change.
Units
Examples:
Replacement check
On the pitch alone: the pressure angle (20° or 14.5°), the profile shift and the face width are checked separately.
All 130 engineering tools
Gears in pumps, winches and gearboxes are ordered by module and number of teeth, inch gears by diametral pitch (DP). Count the teeth and measure the outside diameter, and the identifier gives the module, matches it to the standard series and to a whole DP, names both readings where they lie close and writes the RFQ line.
The calculation holds for a spur gear without profile shift. A profile-shifted gear or one with worn tips gives a module off the series; then the drawing or the mating gear decides.
How the sizes relate
Module, pitch, diameter.
DP is teeth per inch
Inch gears give the diametral pitch, teeth per inch of pitch diameter: DP = 25.4 / module. Module 2.5 and 10 DP differ by under 2 %.
Off the series?
A result far from both a module and a DP points to profile shift or worn tips; then the drawing, the mating gear or a tooth measurement decides.
| Module | Pitch, mm | DP | Outside, 20 teeth | Outside, 40 teeth |
|---|---|---|---|---|
| 1 | 3.142 | 25.4 | 22 | 42 |
| 1.25 | 3.927 | 20.32 | 27.5 | 52.5 |
| 1.5 | 4.712 | 16.93 | 33 | 63 |
| 2 | 6.283 | 12.7 | 44 | 84 |
| 2.5 | 7.854 | 10.16 | 55 | 105 |
| 3 | 9.425 | 8.47 | 66 | 126 |
| 4 | 12.566 | 6.35 | 88 | 168 |
| 5 | 15.708 | 5.08 | 110 | 210 |
| 6 | 18.85 | 4.23 | 132 | 252 |
| 8 | 25.133 | 3.18 | 176 | 336 |
| 10 | 31.416 | 2.54 | 220 | 420 |
| 12 | 37.699 | 2.12 | 264 | 504 |
| 16 | 50.265 | 1.59 | 352 | 672 |
| 20 | 62.832 | 1.27 | 440 | 840 |
| 25 | 78.54 | 1.02 | 550 | 1050 |
| 32 | 100.531 | 0.79 | 704 | 1344 |
| 40 | 125.664 | 0.64 | 880 | 1680 |
| 50 | 157.08 | 0.51 | 1100 | 2100 |
Outside diameter = module x (teeth + 2) for a gear without profile shift.
Sources
Module, circular pitch and DP = 25.4 / module: Wikipedia, "Gear", with its preferred modules. The first series of modules: bdgears on GB/T 1357, aligned with ISO 54. The outside diameter of a standard gear, m(z + 2): KHK’s gear terminology and Firgelli’s gear blank calculator.
Before you send the request
Questions about gears in an RFQ
How do I find the module of a gear?
Count the teeth and measure the outside diameter: module = outside diameter / (teeth + 2). A 30-tooth gear of 64 mm is module 2.
What is the difference between module and DP?
Module is the pitch diameter per tooth in millimetres, DP the teeth per inch of pitch diameter: DP = 25.4 / module, so 8 DP is module 3.175.
Why are two readings shown?
Some module and DP sizes lie within 2 % of each other, such as module 2.5 and 10 DP (2.54 mm); a caliper may not separate them; the drawing does.
What should the request include?
The number of teeth, the outside diameter, the face width, the bore and keyway, the material, and the machine with the mating gear; a photograph helps.
Module found?
Send the line with a photograph of the gear.
A calculation is a cross-check, not proof. Attach photographs of the gear and the mating gear, and Vessel Core checks them before an offer goes back.
Buyer tools
