Taking a broken belt and laying it out flat is not a good way to measure it. You will get the wrong size everytime. (But some times it will still work as there will be enough play in the tensioner.)
V-belts have two length measurements. And inside diameter and outside diameter. Depending on belt width (A/4v-series; B/5v series; C/6v series; etc)....the ID and OD measurement of the belt can be 2-4" difference.
When you take a broke belt and lay it out flat.....the ID and OD become the same you only have one measurement. And that measurement you come up with is acutally somewhere in between the two.
For example.....On B-series belts of the ~60" range.....there is a 3" difference between ID and OD. LEts say your application calls for a B-60 belt, which is a 60" inside diameter belt. (Which is the same belt as a 5v630). That belt will have a 63" outside diameter. Cutting that belt in half and measuring it would give you something in the 61-62" range. So if you went and bought a B-62, your new belt would be 2" too long. IF you got a 5v620 (also a 62" belt), your belt would be 1" too short.
SO you have to know how belts are measured.
IF you are unfamiliar with belts
