This web page contains a live and functional spreadsheet created with
Spur Gear Size Estimator
If your gear is of an industry standard size, this calculator may help identify it. Gears from mass produced commerial products may use non-standard bespoke gears only available from the manufacturers agents.
The size of a metric gear is referred to by the ISO standard 'Module'. Module relates the number of teeth to the pitch circle diameter (PCD). The larger the module number, the larger the gear tooth.
The size of an imperial gear is referred to as DP (Diametral Pitch). It is how many teeth will fit on 1" of the gear cirumference. The larger the DP number, the smaller the gear tooth.
Measure the overall tip diameter of the gear (mm)
Count the number of teeth on the gear
Estimated MOD Size
Estimated DP Size
Note: Gears with a small number of teeth i.e. <15 may give poor results. Some gears may give an equally good result for both metric and imperial and thus uncertain. Just 0.2mm error on measuring the diameter of a small gear can shift the results from MOD to DP. Allow for gear wear when measuring the diameter and take care when measuring gears with an odd number of teeth
Disclaimer: Whilst we have taken evey care to ensure this calculator gives the correct answer, we cannot be held responsible for any errors and their consequencies.