The ideal kickboard size will depend on the swimmer's height, weight, and arm length. However, most boards are between 18 and 20 inches long, and 14 and 16 inches wide.If you're unsure which size to choose, it's best to err on the side of larger rather than smaller. A kickboard that is too small will be difficult to use, while one that is too large may be unwieldy and difficult to control.