# Determining belt length

Hi, Please apologize the stupid question, but what’s the correct way to determine the belt length WITH an IDLER pulley. I measured the inner length of the belt band (see below) but I’m not sure if this is right!?

Seems legit.

Got to say, That’s awesome…

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Nah, yeah somehow. The measurement just shows where I measure the belt length. I am not sure if measuring the belt length on the inner side is correct. I would assume the neutral axis is what I have to take into account.

Count the teeth multiply by 5… Belt length.

The issue is, I set the amount of teeth in the model. So, the difference between 62 and 63 for example is so minimal but gives you a different belt length. I need to know where the band length is measured and then I’ll apply the corresponding number of teeth which you can figure out e.g. here:

https://www.bbman.com/belt-length-calculator/

The total length of a tooth including space between teeth is 5mm

Meaning a 2 tooth belt is 10mm. A 40 tooth belt is 200mm. Model your belt like this? From the inner face of the belt at the surface of the gaps is where it’s measured

Yeah, maybe I could do this. Just need some restructuring.

Measure from this surface marked in pink… sorry for the shitty finger line

This is what I did so far …

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Ok, I think I found it. The belt length is referred to the pitch length (sort of neutral axis) and not to the inner belt length. That’s why I had some discrepancies in the model.

Fits now

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