Abstract: A mail measurement apparatus in the form of a generally rectangular prism having four sides and front and back surfaces. At least one of the sides includes an indentation with a specific depth and a specific breadth. When the side is placed against a flat surface, the indentation creates a gap between the apparatus and the surface. The depth of the gap corresponds to a maximum allowed thickness for a class of mail, while the breadth of the gap corresponds with either the maximum allowed width of length associated with the same class of mail. The other sides of the apparatus may include additional indentations of varying sizes which may correspond to other predetermined maximum dimensions allowed by a postal carrier for the same or other classes of mail.