Can I use a backstroke ledge?

Only if your state association has adopted them. Under NFHS Rules 2-7-2b, 2-7-3 and 8-1-2 (added for 2025-26):

• Backstroke starting ledges may be used only where the state association has a policy allowing them. Some states, such as Idaho, don't allow them.
• The pool must be at least 6 feet (1.84 m) deep from the starting end out to 16 feet 5 inches (5 m) from the end wall.
• Ledges are optional equipment. A host school may choose not to provide them, and that isn't grounds to disqualify anyone.
• If ledges are used in competition, they should also be available during warm-up.
• If there's no state policy, the Referee should have ledges removed.