Pulley & Belt Calculator

Belt length, speed ratio, belt speed and wrap angles. Pick a belt profile to get the nearest standard belt and the pulley sizes for the speed you need.

Standard

Belt type

Driver Ø

Driven Ø

Use datum (pitch) diameters for V-belt pulleys.

Driver speed

RPM

Power

Motors: 1450 / 2900 RPM (50 Hz), 1750 / 3450 RPM (60 Hz). Power is optional.

I know the

Center distance

Drag the pulleys: centre to move, rim dot to resize

Standard belts

Belt	Length	Center distance	Change

Pulley sizer

Enter the speed you need. Combinations use standard pulley sizes and are sorted by speed error.

Target driven speed

RPM

Driver pulley

Driver	Driven	Speed	Error

Multiple Pulley Sets – RPM Reduction

Chain several belt drives on shared shafts. The driven pulley of each set sits on the same shaft as the driver of the next. Starts from the driver speed above.

Number of sets

How it is calculated

The calculator uses the exact open-belt geometry, not the common approximation. R and r are the large and small pulley radii (pitch or datum), C is the center distance. Timing pulley pitch diameter is d = z · p / π.

φ = asin((R − r) / C) Belt length L = 2·C·cos φ + R·(π + 2φ) + r·(π − 2φ) Wrap angle small = 180° − 2φ, large = 180° + 2φ Speed ratio i = D_driven / D_driver Driven RPM n₂ = n₁ · D_driver / D_driven Belt speed v = π · D_driver · n₁ / 60 000 (m/s, D in mm) Shaft torque T = 9549 · P / n (N·m, P in kW) Belt pull Fe = 1000 · P / v (N, effective tension)

Standard V-belt lengths shown are ISO preferred datum lengths (R40 series). Belt makers also stock many sizes in between, so check their catalogue. Pulley sizes follow the same R40 series. Minimum datum diameters: SPZ 63 mm, SPA 90 mm, SPB 140 mm, SPC 224 mm. Narrow V-belts are usually rated up to about 40 m/s and need at least 120° wrap on the small pulley. Timing belts need about 6 teeth in mesh on the small pulley.