Standard baby crib mattresses are not all sized identically, but instead range in width from 27 5/8 inches to 28 5/8 inches and range in length from 51 3/4 inches to 53 inches. A baby crib mattress is usually between 4 and 6 inches thick.
Baby crib mattresses include both foam mattresses and coil mattresses. When choosing a crib mattress, parents should find one that fits into the crib snugly and leaves a space smaller than two adult finger widths on each side. Most baby crib mattresses are firm to ensure infant safety and comfort. Standard baby crib sheets are typically sized to accommodate most infant crib mattresses.