Timing Belt Calculator

Inputs

View results
GT2 = 2 mm, GT3 = 3 mm, HTD-5M = 5 mm, T5 = 5 mm, XL = 5.08 mm.
mm
Teeth on the driving pulley (on the motor / input shaft).
teeth
Teeth on the driven pulley (on the output shaft).
teeth
Distance between the two pulley centres.
mm
Optional stock belt tooth count. Enter 0 to use the nearest whole tooth count from the calculated length.
teeth
Optional — for belt speed and driven RPM. 0 to ignore.
rpm

Results

Default result
Edit inputs
Belt pitch length(L)
260.4mm

2C + (π/2)(D₁+D₂) + (D₂−D₁)²/(4C).

Also computed

Theoretical belt teeth(z_exact)130.2teeth

Calculated pitch length divided by belt pitch before rounding.

Belt length in teeth(z_b)Pass130

Nearest standard size is 130 teeth (theoretical 130.20); set the centre distance from that belt.

Nearest whole tooth count — pick the closest standard belt.

Selected / nearest belt(z_sel)Pass130teeth

130-tooth nearest belt; enter an actual catalog belt if needed.

Uses the entered stock belt tooth count, or the nearest whole count when set to 0.

Selected belt pitch length(L_sel)260mm

130 teeth x pitch.

Selected belt teeth times belt tooth pitch.

Center distance for selected belt(C_sel)Pass99.8mm

Center distance that fits the 130-tooth nearest belt.

Back-solved center distance for the selected whole-tooth belt.

Center distance shift(ΔC)−0.2031mm

Negative means closer; positive means farther apart.

Move from the entered center distance to fit the selected belt.

Method notes 5 notes
  • Pitch diameter D = N·p/π, where N is the pulley tooth count and p the belt tooth pitch (GT2 = 2 mm, GT3 = 3 mm, HTD-5M / T5 = 5 mm, XL = 5.08 mm).
  • Belt pitch length L = 2C + (π/2)(D₁ + D₂) + (D₂ − D₁)²/(4C) for an open (non-crossed) belt; length in teeth = L / p.
  • In practice you pick a standard whole-tooth belt, then back-solve the centre distance to suit it — an idler, slotted mount or spring tensioner takes up the small difference.
  • Small-pulley teeth in mesh is a quick screen only. Belt width, tooth profile, torque, pretension and manufacturer ratings still control capacity.
  • Speed ratio i = N₂ / N₁ and driven speed n₂ = n₁ · N₁ / N₂. A toothed belt does not slip, so the ratio is exact.

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