Help with belt length calculation?

Hi guys,

I’m trying to figure out how to calculate the length of belt that I need. I can’t seem to get the Spd-si calculator to show up, and I’m not sure where else to find a reliable belt calculator. I am using a drive ratio of 17T to 40T with a center distance of 60mm. I am trying to find a 15mm wide belt as well.

also @psychotiller mentioned to me that he’s adding one to his site. I’d like to have one on mine too sometime soon since this is a very commonly needed tool.


I need one that works with an idler pulley!

1 Like

Not sure that one exists. Use your math young Jedi. Or order your belt a little big. Each tooth on your belt is equal to 5mm in length with 5mm htd.

1 Like

I’m going with htd3m, and I don’t know how the Math works.

If I had to take a guess I would say 3mm htd = 3mm of belt length. Use the BnB calulator linked on my site and figure out the radius of your idler (distance from its center to where it pushes the belt into.) you should be able to calculate how many extra teeth in belt you need. -Also, remember the motor has 4.5 mm of adjustability. That can take up quite a bit of slack.

You can always order a new belt too. They’re really inexpensive.