What this tool calculates
Translate pulley tooth counts and center distance into a whole-tooth synchronous belt size before ordering or modeling tension adjustment.
Formula and method
Pitch diameters are teeth × pitch ÷ π. Open-belt length ≈ 2C + π(D₁ + D₂) ÷ 2 + (D₂ − D₁)² ÷ (4C). The result is rounded to the nearest whole tooth, then the matching center distance is solved from the same relation.
When to use it
Use this for fixed or adjustable two-pulley layouts when choosing a stocked closed-loop belt or checking a CAD center distance.
Worked example
Two 20-tooth GT2 pulleys at 200 mm center distance require a 440 mm pitch-line belt, exactly 220 teeth.
Assumptions and limitations
This is an open, uncrossed two-pulley drive measured at the belt pitch line. Tensioning travel, minimum pulley wrap, idlers, belt thickness outside the pitch line, and manufacturer installation allowances still need a mechanical check.
Common mistake
Do not use outside pulley diameter in place of pitch diameter, and do not order a fractional-tooth belt.