How do I size a ring at home without getting it wrong?

Measure an existing ring that already fits the intended finger rather than the finger itself: place it on a printed sizing chart or measure its inside diameter with a ruler, and match that to the seller’s own chart. Fingers change size through the day and with temperature, so measure the finger only in the afternoon at room temperature, and take the larger reading if you fall between sizes. Wide bands sit tighter than narrow ones — go up a quarter to a half size for anything over about 6 mm. Before ordering, ask two things: what the return window is, and whether the design can be resized at all. Eternity bands, pavé shanks and engraved rings often cannot be, which turns a sizing mistake into a returns problem instead of a workshop visit.