Technically, the average length of a tractor trailer is 50 feet and 6 inches. However, this is due to the fact that there are two standardized lengths of trailer.
The standardized lengths for a trailer to be pulled by a semi-truck are 48 feet and 53 feet. However, the length of a 48-foot trailer with tractor can be minimized by using a short wheelbase tractor, which eliminates some storage from the cab to reduce length. In terms of total length, these trucks are lengths of 71 and 73 feet with a possibility of being only 65 feet using a short wheelbase tractor.