Aspect Ratio
The dimension of a mailpiece expressed as a ratio of length (the direction parallel to the address) divided by height. For example, a postcard 5-1/2 inches long by 3-1/2 inches high has an aspect ratio of 1.57. An aspect ratio between 1.3 and 2.5, inclusive, is required for automation compatibility. For First-Class Mail letters, aspect ratio determines whether a nonmachinable surcharge applies.