You'll need to know your native rotor size for your fork and bike frame and the size rotors you will be running. For example, Fox 36 is a 180 post mount, so if you want to run 203mm rotors you'll need a +23 adapter. You can always reach out via email on the website and we can help you through it.
@@bb7115 it’s not really possible to measure the adapter itself because there are multiple different dimensions that can achieve the same affect. The posts are also typically not the same size. The best way to determine what size you need is based off of the actual bikes post mounts subtracted from the desired rotor size.