INNERLIG Spring mattress for extendable bed 38 1/4x74 3/4 ". One mattress ‒ three lengths. With the help of the 2 extendable parts, the mattress can grow with your child, from 47" to 61" or 74¾". The outer cover is easy to remove and is machine washable at 140°F (Hot). Fits all our extendable beds.