These belts are flat to look at with raised ribs running along the inside in the direction that they run or drive. Poly V belts are sometimes called poly vee, multi v, multi vee, multi ribbed or even micro v. Metric sizes are normally prefixed with the belt rib type before the belt number and imperial belts will normally have the size first followed by the belt type.
To measure a poly V drive belt is easiest if you can just measure end to end. Then measure the width and then how many raised ribs across the belt. This will tell us everything we need to identify your belt. The problem comes with the small polyurethane drive belts found on many planers and belt sanders. These are very tricky to measure and a lot easier to offer up against another belt. We really recommend that you post us a sample have a good look for a model number on your machine and we may already know which belt you require.