The three measurements you need to measure and write down are the following,
(1) Outer circumference and I know a few belt manufacturers measure the circumference at the cord instead of outer circumference. So what you measure outside may not be accurate and yet others have a certain load on the belt when measuring outer circumference.
For this tutorial we will just stick with outer circumference.
(2) Width of the belt and you have to be careful here as just dropping a caliper across the belt and measuring the width may not be correct as if the manufacturer trims the edges of the belt you will not have a accurate width.
When you just drop a caliper on the width you are measuring the trimmed width, While putting a straight edge on each of the side the belt and measuring across the rib from straight edge to straight edge you would arrive at projected width.
This is shown below in the belt width image.
(3) Angle of the face of the belt, Not all clutch faces have the same angle so when measuring or selecting a alternate belt make sure to measure the angle of the belt from outer ribs to inner ribs and compare to oem.
This image shows outer circumference as well as cord circumference.
You can put a mark on the belt and roll on a floor and when that marks comes around just put a dot on the floor and measure the length and you will have the circumference.
You can wrap a string around the belt and mark it and measure the string length.
You can use a fabric tape measure for sewing.
This image shows what I was referring to on belt width and how just using a caliper may give you a incorrect measurement.
Just as an addition here is a image that somewhat give you an idea how a belt deflection that is not set correctly affects cvt performance.
