Belt Steps per mm Calculator

What this tool calculates

Turn motor and GT-style belt hardware into firmware-ready motion values before changing an X or Y axis.

Formula and method

Full steps/rev = 360 ÷ motor step angle. Steps/mm = full steps/rev × microsteps × motor-to-output ratio ÷ (belt pitch × pulley teeth). For a direct belt drive, Klipper rotation_distance is belt pitch × pulley teeth.

When to use it

Use this after changing a motor, stepper-driver microstep setting, drive pulley, belt pitch, or reduction stage. The result is a theoretical starting value for Marlin M92 or an equivalent firmware setting.

Worked example

A 1.8° motor at 16 microsteps driving a 20-tooth GT2 pulley travels 40 mm per revolution. It needs 3,200 microsteps per revolution, so the result is 80 steps/mm and 0.0125 mm per microstep.

Assumptions and limitations

The belt is synchronous, pulley tooth count is correct, and the entered ratio is motor revolutions per output revolution. Theoretical microstep distance is not guaranteed positioning accuracy. Belt stretch, pulley runout, frame compliance, driver current, and lost steps remain mechanical limits.

Common mistake

Do not use a driver’s internal 256× interpolation when firmware is configured to send 16 microsteps.