Provided is a video decoding method including: generating coding units by splitting at least one of a height and a width of a largest coding unit having a first size; based on whether a height or a width of a non-square first coding unit including an outer boundary of an image, among the coding units, is greater than a maximum transform size, determining whether it is allowed to generate two second coding units by splitting at least one of the height and the width of the first coding unit; and decoding the second coding units generated from the first coding unit.