The size you want to order depends on the preferred fit.
3 different fits possible. Measure the wrist or ankle around the bones. Don't pull the tape tight, just ensure it lays smoothly and flat around the wrist.
a. Add in 1/4 inch for a close fit, like a watch band b. Add in 3/8ths inch for a looser bracelet like fit c. Add in 1/2 inch for a very loose bangle like effect.