Ambient temperature and the time of day among other factors can affect the fit of a ring. We offer a ring sizing template which will help you determine what size ring to order. Print this out, being careful to follow the instructions, including matching the INSIDE of a ring the size of which you want to fit with the outside of the template. That should give you your ring size. While this will typically work well, the best answer is to visit a jeweler (who will usually do this for free), and have them size your finger for the most accurate fit.   Ring Sizing Template