The AS-568* Standard O-Rings Quick Reference Chart lists every AS-568 Standard size O-ring — listed in inches, with inside diameters (ID) from 1/32 to 26 in., outside diameters (OD) from 3/32 to 26½ ...

Aside from the paper ring size chart, one of the most accurate at-home sizing methods is a ring sizer. Ring sizers can be found online for as cheap as $4. The process is quite simple: "you feed one ...