Choosing a crib mattress isn't the same as buying a mattress for yourself. Instead of flopping down on potential picks to test their comfort level, you must find a mattress that safely fits your baby's crib. The American Academy of Pediatrics states on HealthyChildren.org that parents and caregivers should always ensure the baby furniture they choose meets the most current safety requirements.
Between the Crib
The Consumer Products Safety Commission defines the standard size for a full-size baby crib as 28 inches wide by 52 3/8 inches long, plus or minus 5/8 inch for both width and length. At a minimum, the mattress should be 27 1/4 inches wide by 51 1/4 inches long, and it should be no thicker than 6 inches. A full-size crib, it explains, is one that is designed to provide sleeping accommodations for an infant and is intended for use in the home, a child care facility, a family child care home or in places of public accommodation affecting commerce.
Checking for Fit
At best, the mattress should press up against the crib's rails so that there is no gap or space between the side of the mattress and the side of the crib. A gap the width of two adult fingers is excessive, according to the commission.