Inexpensive yet very handy measuring tool for ring sizes. Sizes 4-13 in half size increments.
To ensure an accurate ring size (or an accurate size on any circular jewelry piece), add the wire diameter (or the bar-stock thickness) to the finished inside diameter you want and multiply by pi (3.14).
1 Start with the desired inside diameter of the finished ring.
2 Add the wire diameter or metal thickness.
3 Multiply the result by pi (3.14).
4 This is the length of material you will need to cut to achieve your desired final result.