Typically, small barrels are suitable for short to medium hair, while medium and large barrels work well for medium to longer locks.
If you’re going for tight, bouncy curls, a smaller barrel curling iron (1/2- to 1-inch) is your best choice. If you prefer a more relaxed style with loose waves or big, bouncy curls, then a medium (1.5-inch) to large barrel (2-inch) would be perfect.
Coarse or thick hair typically holds larger curls better than fine hair so you can use bigger iron sizes. If you have fine or thin hair, using a smaller barrel might be more effective in maintaining the curl.