The best way to get a good fit is to measure a cuff bracelet you already have and compare the inside end-to-end measurement and the gap measurement with those of the bracelet you are considering purchasing.
If you do not have a cuff bracelet to use for comparison, then follow this method:
For example, if your wrist measures 7" and you are looking at a bracelet with a 5-3/4" inside circumference and a 1-1/4" gap, then the bracelet will probably fit. How well it will fit will depend on whether you like to wear your cuff bracelet tight or loose, alone or with other bracelets, in front of or behind the prominent bone on your wrist. Therefore, you may want to add 1/2 inch to 1 inch to the measurement depending upon these variables.
Many cuff bracelets are adjustable. They can be opened or closed up to about a 1/2 inch larger or smaller. The types that are not easily adjustable are those that are made from very thick, heavy silver or those with inlaid stones across the entire front and sides.
To adjust your bracelet, be very careful how you adjust it so you do not damage it. If you try to bend an area of your bracelet where there is a stone or inlay, the stone may pop out or the inlay may crack. Changing the underlying structure on an inlay bracelet, may cause the inlay to pop out immediately or at a later date.
To determine your bracelet size for a link style bracelet: measure your wrist where you want the bracelet to lay for the total length of the bracelet. If you prefer a snug, wrist-hugging fit, use the actual measured circumference of your wrist. If you like a draping, looser fit, increase your measurement by a 1/4" to 3/4" depending on your taste. Keep in mind that larger-link or chunky bracelets may fit more tightly than thin bracelets.