Most baseboards are 1/2 to 1 inch thick and 3 to 8 inches tall. Gauge baseboard size by its relationship to crown and casing. Baseboard is typically taller than casing is wide, and about as tall as the crown. The taller the crown, the taller the baseboard should be to maintain visual balance. A standard 8-foot wall typically has a baseboard 3 to 5 inches tall, while a 10-foot ceiling calls for 5 to 7 inches.