A crib bumper for a standard-size crib is about 27 inches long on the short sides and about 54 inches long on the long sides. For a portable crib, the crib bumper is about 25 inches long on the short sides and about 40 inches long on the long sides.
The height of crib bumpers can vary, but is generally about 8 inches. Crib bumpers became popular when the slats in cribs were far enough apart for a baby's head to become trapped between them. All cribs sold now in North America are require to have slats close enough together so that a baby's head won't fit through. Several child safety organizations recommend against using crib bumpers because they pose a risk of suffocation and strangulation to the baby.