Crib Mattress Fit

Follow these safety guidelines to make sure you have the proper crib mattress dimensions!

Kolcraft Roscoe 3 in 1 Convertible Crib

Buying a crib is an exciting part of your journey into parenthood — and one that many parents-to-be tackle before purchasing a crib mattress. To meet ASTM safety regulations, crib mattresses must fit properly inside USA-standard full-size cribs and toddler beds. It’s important to measure the inside dimensions of your crib to ensure that it meets these safety standards.


  • Minimum standard crib mattress dimensions are 27 1/4″ wide x 51 5/8″ long. The baby mattress should always fit snugly inside a standard-sized crib. All Sealy Baby crib mattresses are sized to fit the standard-sized crib and follow ASTM regulations.
  • All crib mattresses must not exceed 6″ in height when measured from seam to seam. This helps to ensure that babies cannot climb out of their crib as they grow.
  • Crib mattresses are designed to be slightly smaller than standard crib dimensions. Ensure that there is no more than a 1″ gap between the mattress and crib wall.
  • Be sure to look at product measurements instead of shipping measurements to be sure of the actual mattress size. Don’t purchase “mini crib” mattresses made exclusively for mini cribs, they will be too small.


  • Measure the INTERIOR of your crib to the below specifications. If your crib measures any smaller or larger, please contact the crib manufacturer as your crib does not meet crib regulations.
  • Crib dimensions are dictated by ASTM and Federal Law. The dimensions in the crib standard require cribs to have interior dimensions of 28″ wide and 52 3/8″ long; these ‘standard’ crib dimensions can vary by plus or minus 5/8″. Mattresses are designed to be slightly smaller to allow them to fit within these dimensions.