This is off of Ford's towing website.
maximum loaded Trailer weight
(as shown in the Trailer Towing Selector charts pages 16?24) is
the highest possible weight of a fully loaded trailer the vehicle can tow, based on a minimum towing vehicle GVW. It assumes a towing vehicle with any mandatory options, no cargo, tongue load of 10-15% (conventional trailer) or king pin weight of 15-25% (5th-wheel trailer), and driver only (150 lbs.). F-Series Super Duty? Chassis Cab models also assume a second-unit body weight of 1,000 lbs. Weight of additional options, passengers, cargo and hitch must be deducted from this weight.
Stan