TOOLS / DRIVES

Pulley and belt length calculator

Work out open-belt length, drive ratio, driven speed and wrap angle from pulley diameters and centre distance.

Belt pitch length (open belt)1476.24 mm

Ratio 2.00 : 1 · driven speed 720 RPM · wrap on small pulley 168.52° · belt speed 15.08 m/s

Geometry only — this length does NOT rate the belt for power. Belt power capacity, groove profile and tension come from the belt maker's tables (ISO 4183 groove context); keep wrap on the small pulley above about 120° where possible.

Formula

Belt length L = 2C + π(D + d)/2 + (D − d)²/(4C). Ratio = D/d. Wrap on the small pulley = 180° − 2·arcsin((D − d)/(2C)).

Standard / source

Standard open-belt geometry; V-belt groove profiles and lengths are covered by ISO 4183 and the belt maker's catalogue.

Worked example

Driver 200 mm, driven 100 mm, centre distance 500 mm, driver 1440 RPM: L = 1000 + π × 300/2 + 100²/2000 ≈ 1476.24 mm. Ratio 2:1, driven speed 720 RPM, wrap ≈ 180° − 2 × 5.74° ≈ 168.52°.

Safety note

Geometry only — this length is NOT a power rating. Belt power capacity, groove profile and tension come from the belt maker's tables; a belt that fits geometrically can still be overloaded. Keep guards in place on running drives.