Belt Length & Centre Distance Calculator
Work out the belt length for a two-pulley drive from the pulley diameters and centre distance — or flip it around and find the centre distance you need for a given belt. Works in metric or imperial.
How the belt length formula works
For an open belt drive with two pulleys, the belt length L is found from the driver pulley diameter D, the driven pulley diameter d, and the centre distance C:
The first term accounts for the two straight runs of belt between the pulleys. The second is the belt wrapped around the two pulleys (the average of their circumferences, weighted by contact). The third term corrects for the difference in pulley sizes — the belt wraps more than half of the larger pulley and less than half of the smaller.
Run it in reverse — give us the belt length and both pulley diameters — and the calculator solves the same formula as a quadratic to find the centre distance you need to set up.
Once you have your result, use Get a price on this belt to send the dimensions straight to our team for a quote.