Gear ratio and pitch diameter calculator

Get gear ratio, output speed, pitch diameters and centre distance from module and tooth counts.

Module (mm)Driver (pinion) teethDriven gear teethInput speed (RPM)

Gear ratio2.00 : 1

Pitch diameters 40.00 mm and 80.00 mm · output 500 RPM · centre distance 60.00 mm

Metric module system (ISO 54). This gives ratio and pitch geometry only — tooth strength, backlash, profile shift and guarding/overspeed checks for safety-related drives need the gear maker's data and a qualified check.

Formula

Pitch diameter = module × teeth. Ratio = driven teeth / driver teeth. Output RPM = input RPM / ratio. Centre distance = (PD1 + PD2)/2.

Standard / source

Metric module gear system, ISO 54 (cylindrical gears — module series). Imperial diametral-pitch gears are a different system and are not covered here.

Worked example

Module 2, pinion 20 teeth, gear 40 teeth, input 1000 RPM: pitch diameters 40 mm and 80 mm, ratio 2:1, output 500 RPM, centre distance 60 mm.

Safety note

Ratio and pitch geometry only — not a strength rating. Tooth strength, backlash, profile shift and guarding/overspeed checks for safety-related drives need the gear maker's data and a qualified check.