Definitely worth the cost. My weight goes up and down a bit, so my ring sizes change and i have no idea what size my rings are that fit. This ring size gauge is going to save me a lot of headaches and returns, and even on return shipping. Also a handy thing to have to get the ring sizes of other people you buy rings for as gifts. Find out their size in advance and avoid disappointments! I think the only thing that makes any ring gauge inaccurate is if the band of the ring is super wide. In that case, go up a size for a more comfortable fit. I wish I had bought this years ago!