A cock ring is one of those things that just about everyone has heard of, has seen or possibly knows how to use properly. When used correctly, cock rings not only give you a harder erection but they also make orgasms feel even better.
On the darker side, improper use of cock rings can lead to pain and injury. So you want to know what you're doing up front.
If you want to use a cock ring that is not adjustable you must measure to know the proper size to purchase.
To measure for the proper fit: Take a string and slip it behind the balls and tug it up around the top of your penis (where it meets your body). Mark the string on both ends where it comes together at the snugness that is comfortable for you. This measurement will give you the circumference. Now take your circumference measurement and divide it by pi (3.14). This measurement will give you your diameter of ring size. It is recomended that measure a couple of times to insure proper size measurement.