It took me 3 different local autoparts stores to find the right length v-belt for my custom passenger side ac compressor set up on my Regal and then I ended up ordering the same length but a little wider in a Continental belt from Summit and took the local one back.
It use to be we took a string to measure the length and headed to the store with the measurement on a piece of paper and got the belt we needed by measuring the belt with a tool like this..