A truck's owner's manual lists its towing specifications, which includes towing instructions and limitations, towing capacity, and safe towing tips. The specifications to manually calculate the towing capacity are located on the compliance certification sticker. This sticker is found on the truck's driver's side door jam.
To determine a truck's towing capacity manually, locate the combined gross vehicle weight rating on the compliance certification sticker. Next, determine the weight of the vehicle along with all cargo, fuel and passengers to find the loaded weight. Finally, subtract the loaded weight from the combined gross vehicle weight rating. The resulting figure is the vehicle's towing capacity.