It's important to know the brace height of a recurve bow so you can select the correct string. Too low a brace height, and the bow will not have full power when drawn. If the brace height is too high, the bow will be overdrawn, and it may stress the material and damage the bow. The recurve bow will have a recommended brace height given by the manufacturer, but it may vary by model number.
Check the instructions that came with the bow for the manufacturer's recommended brace height.
Place the bow square in the pivot point of the bow. This is the narrow part of the bow near the handle.
Measure the distance between the narrowest part of the bow and the bow string at a 90 degree angle. This is the bow's brace height.
If the bow's brace height is just a little too high, you can shorten the bowstring by unstringing the bow and giving the bowstring a few clockwise twists.