The United States Postal Service sets size and weight limits for boxes and other parcels. When you add the length of a box to its girth, the total may not exceed 108 inches and the weight cannot be more than 70 pounds. For some shipping services like Parcel Select, size and weight limits are smaller.
USPS Shipping Girth
Use a measuring tape to find the height, width and length of the box in inches. For USPS shipping, the length is always the longest dimension of the box. Multiply the width by 2 and multiply the height by two. Add the results together to find the girth. For example, suppose you measure the height of a box as 10 inches, the width as 12 inches and the length as 60 inches. Multiply 10 inches by 2 and 12 inches by 2. Add the results. The total of 44 inches is the girth of the box. Add the 60-inch length to the 44-inch girth for a total of 104 inches. The box in this example is within the USPS 108-inch size limit.