Belt Length Calculator

Inputs

Center distance (C)

Distance between the two pulley centres.

Small pulley diameter (D₁)

Pitch diameter of the smaller pulley.

Large pulley diameter (D₂)

Pitch diameter of the larger pulley.

Default result

Belt length(L)

1,080mm

2C + (π/2)(D₁+D₂) + (D₂−D₁)²/(4C).

Also computed

Wrap angle (small pulley)(θ₁)160.8°

Adequate wrap for good grip.

Contact angle on the smaller pulley — the limiting pulley for grip.

Wrap angle (large pulley)(θ₂)199.2°

Method notes 2 notes

Belt length L = 2C + (π/2)(D₁ + D₂) + (D₂ − D₁)²/(4C) for an open (non-crossed) belt; use the pulley pitch diameters.
The wrap angle on the small pulley sets the grip — keep it above about 120° to limit slip. Round the length up to the nearest standard belt, then set the centre distance from the belt you choose.