What tongue weight is
Tongue weight is the part of the trailer's weight that presses down on the hitch ball. On a fifth wheel or gooseneck it is called pin weight and presses on the hitch in the bed. The rest of the trailer's weight sits on the trailer's own axles.
A common guideline is 10 to 15% of the loaded trailer weight for a conventional trailer, and 15 to 25% for a fifth wheel or gooseneck. The percentage changes with how you load the trailer: weight ahead of the trailer axles adds tongue weight, weight behind them takes it away.
How it is calculated
tongue weight % = tongue weight ÷ trailer weight × 100
guideline range = trailer weight × 10% to trailer weight × 15%Example: a 6,000 lb trailer with 700 lb on the hitch is at 700 ÷ 6,000 × 100 = 11.7%. For that trailer, the 10 to 15% guideline gives 600 to 900 lb. A 12,000 lb fifth wheel with 2,400 lb of pin weight is at 20%, and the 15 to 25% guideline gives 1,800 to 3,000 lb.
The bathroom scale method
A bathroom scale cannot hold a tongue load, but a lever divides the load. Put a short pipe under one end of a sturdy board and the scale under the other end, a distance D apart. Rest the coupler on the board at a distance A from the pipe. Taking moments about the pipe:
tongue weight = (scale reading − board alone) × D ÷ AWorked example: D = 36 inches and A = 12 inches, so the factor is 3. The scale reads 233 lb, and it was zeroed with the board on it. The tongue weight is 233 × 36 ÷ 12 = 699 lb. Keep the coupler at the same height as when hitched, keep the trailer level, and check that the reading is inside the scale's range. If you rest the tongue jack on the board instead of the coupler, the reading comes out slightly high, because the jack sits behind the coupler.
What to check
The tongue weight counts against your truck's payload and GVWR, and against the tongue weight rating on the hitch label. A public truck scale or a tongue weight gauge gives a direct reading.
Questions
How do you calculate tongue weight percentage?
Divide the tongue weight by the loaded trailer weight and multiply by 100. 700 lb on a 6,000 lb trailer is 11.7%.
What should the tongue weight be for a 6,000 lb trailer?
A common guideline for conventional trailers is 10 to 15%, which is 600 to 900 lb for a 6,000 lb trailer. Your hitch and truck labels give the maximum they are rated for.
How much pin weight does a fifth wheel have?
A common guideline is 15 to 25% of the loaded trailer weight. For a 12,000 lb fifth wheel that is 1,800 to 3,000 lb. Weigh yours: it depends on how the trailer is loaded.
Can I measure tongue weight with a bathroom scale?
Yes, with a board as a lever. With the pipe 36 inches from the scale and the coupler 12 inches from the pipe, multiply the net scale reading by 3: 233 lb on the scale means about 699 lb of tongue weight.