Hi chaps. Ive used you a couple of times, and have nothing but good remarks to say about the service. keep it up!

I think I have a useful question (well, at-least I think it will benefit me, maybe a few others)

What is the correct actual way of working out belt lengths?

Ive drawn you a nice picture :D
Click image for larger version. 

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I get.... to work out the circumference of the pulley its
teeth x pitch
a=(200x5)1000mm
b=(600x5)3000mm

so ive always gone with (A/2) + B(/2) + (2xC) which I appreciate isnt very accurate.

Im sure there is a smarter way of doing it... to get the perfect belt size. but ive always wondered how?

So you guys are the pro's.... the stage it yours :D