KEVOS® MAKEOS · Power Transmission
Spur Gear Pair Geometry
What nominal geometry and speed ratio follow from module and tooth counts?
Calculate reference geometry and ideal output speed for an unshifted external spur gear pair.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Module | mm | Common transverse module of both spur gears. |
| Driver teeth | teeth | Tooth count of the input gear. |
| Driven teeth | teeth | Tooth count of the output gear. |
| Input speed | rpm | Speed of the driver. |
Method and formulas
- Reference diameter = module × tooth count.
- Nominal centre distance = module × (driver teeth + driven teeth) / 2.
- Speed ratio = driven teeth / driver teeth; output RPM = input RPM / ratio.
- Example: module 2, 20/60 teeth gives 40/120 mm reference diameters, 80 mm centres and 400 rpm output from 1200 rpm.
Limitations
- External spur gears without profile shift; both must have compatible tooth system and pressure angle.
- No tooth-strength, undercut, backlash, contact ratio or lubrication rating.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- spur gear
- module
- gear ratio
Who it is for
- Mechanical designers
What you get
- Driver reference diameter
- Driven reference diameter
- Nominal centre distance
- Reduction ratio
- Output speed
Interpreting the result
- Confirm the manufacturer’s operating centre distance and all rating conditions before selecting gears.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2126–2133. Topic reference; no source tables or recommended settings are reproduced.
- KHK Gears: Calculation of Gear Dimensions — https://khkgears.net/new/gear_knowledge/gear_technical_reference/calculation_gear_dimensions.html
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