Work out timing belt pitch length instantly with clear inputs, formula shown and shareable results.
Belt pitch length is 2C + (pi/2)(D1 + D2) + (D2 - D1)squared/(4C). Because belts come only in whole numbers of teeth, the centre distance normally has to be adjusted to suit a standard belt rather than the other way round.
Belt length
L = 2C + (pi/2)(D1 + D2) + (D2 - D1)^2 / (4C); teeth = L / pitch
Fewer teeth in mesh means each tooth carries more load and the belt is more likely to ratchet. At least six teeth in mesh is the usual minimum.
Pick the belt from the standard range, then set the centre distance to suit it, allowing a tensioner or idler for adjustment.