Boat Trailer Tongue Weight Calculator
Calculate the correct tongue weight range for your boat trailer and check whether your estimated tongue weight falls within the safe 9 to 15 percent range recommended by SAE J684. Enter the gross trailer weight (boat plus trailer plus gear and fuel) and your tongue weight to see whether you need to redistribute load.
Tongue weight formula
Tongue weight % = (Tongue weight / GTW) × 100
Safe range: 9% to 15% of GTW (SAE J684)
Target: 10% to 12%
To increase tongue weight, move heavy items forward of the trailer axle(s). To decrease tongue weight, move heavy items rearward. Never exceed the lowest rating among tow vehicle, hitch, ball mount, and trailer coupler.
Hitch class tongue weight limits
| Class | Max GTW | Max Tongue Weight |
|---|---|---|
| Class I | 2,000 lbs | 200 lbs |
| Class II | 3,500 lbs | 350 lbs |
| Class III | 8,000 lbs | 500 to 800 lbs |
| Class IV | 10,000 lbs | 1,000 lbs |
| Class V | 18,000 lbs | 1,700 lbs |
Always verify ratings on your specific hitch, vehicle, and trailer. These values are general guidance; individual products vary.
Boat trailer tongue weight calculator: frequently asked questions
What is trailer tongue weight?
Tongue weight is the downward force that the trailer hitch applies to the tow vehicle's hitch ball. It is a portion of the total trailer and boat weight. Proper tongue weight is critical for safe towing: too little and the trailer can sway dangerously; too much and the tow vehicle's rear suspension is overloaded and steering is impaired.
What percentage of trailer weight should tongue weight be?
SAE J684 and US trailer towing guidelines recommend tongue weight between 9 and 15 percent of the gross trailer weight (GTW) for conventional trailers. For most boat trailers, targeting 10 to 12 percent provides good stability. A 3,000-lb trailer (boat, trailer, gear, water) should have 270 to 450 lbs of tongue weight.
How do I measure tongue weight?
The most accurate method is a dedicated tongue weight scale placed between the coupler and a support. A bathroom scale on a 2x4 can give an approximation. You can also use the before-and-after vehicle weighing method: weigh your tow vehicle alone, then with the trailer attached at the hitch (only front axle on scale), and subtract the difference.
What happens if tongue weight is too low?
Low tongue weight (below 9 percent) makes the trailer prone to fishtailing or sway, especially at highway speeds. Trailer sway is a leading cause of serious boat towing accidents. Moving heavy items toward the front of the trailer (in front of the axle) increases tongue weight.
What is the maximum tongue weight for a typical hitch receiver?
Hitch receivers are rated by class. Class III hitches (the most common for boat trailers) are typically rated for 350 to 500 lbs tongue weight. Class IV hitches handle 500 to 750 lbs. Always check your specific hitch, tow vehicle, and trailer's individual tongue weight ratings and use the most restrictive limit.
Official sources
- SAE International Standard J684: Trailer Couplings, Hitches and Safety Chains (defines tongue weight as 9 to 15% of GTW).
- NHTSA: Trailer Safety.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.