Calculator guide

How to Calculate Timing Belt Length and Tooth Count

The formula for a closed-loop belt, with a worked example, so you can order the right size the first time.

Two pulleys of the same size

Pitch diameter = teeth x pitch / 3.1416. Belt length is about 2 x centre distance + 3.1416 x pitch diameter. Divide by the pitch to get the tooth count, then round to the nearest whole tooth.

Example: two 20-tooth GT2 pulleys (pitch 2 mm) with a 100 mm centre distance. Pitch diameter = 20 x 2 / 3.1416 = 12.73 mm. Length = 2 x 100 + 3.1416 x 12.73 = 240 mm, which is 120 teeth: a GT2-240 belt.

Two pulleys of different sizes

Length is about 2C + 3.1416 x (D1 + D2) / 2 + (D1 - D2)^2 / (4C), where C is the centre distance and D1, D2 the pitch diameters.

Tips

• Leave a little adjustment range in the centre distance so you can tension the belt.
• Pick the nearest standard length, then fine-tune with a tensioner or idler.
• If you are not sure, send us your centre distance and pulley teeth and we will suggest a length.

See also: GT2 belt length guide · tensioning · all products