The interior dimensions of a standard full-sized crib are roughly 28 inches wide by 52 3/8 inches in length. Non-full-sized baby cribs include those that are collapsible, or non-rectangular in shape. The interior size of such cribs must be significantly larger or smaller than that of a full-size.
As of 2015, the United States Consumer Product Safety Commission has issued federal requirements for the dimensions of both full-sized and non-full-sized baby cribs. Most standard full-sized crib mattresses sold in the United States are 27 1/4 inches by 52 inches, with standard full-size cribs usually measuring 30 inches by 54 inches.
Non-full-size baby cribs must have interior dimensions that are either smaller than 49 3/4 inches by 25 3/8 inches or larger than 55 inches by 30 5/8 inches. The smaller dimension is usually used as the regular size for portable or collapsible cribs, while the large dimension often encompasses cribs that are round or otherwise oddly shaped.
For any crib, the space between slats must not be wider than 2 3/8 inches to ensure that a baby's head cannot get caught in the space. These regulations are kept in place for the safety of infants less than 35 inches tall and under 2 years of age. A taller or older child runs the risk of falling out of a regulation full-sized crib.