Tongue Weight Calculator
Tongue weight below about 10% is the condition that starts trailer sway, and sway at highway speed is very hard to recover from. Knowing you are out of range is only half the problem, though. This calculator also solves the moment balance for you: how far to move a given weight, in which direction, to bring the tongue back into range.
- Tongue weight
- 8.6% Below the 10% minimum — this is the sway condition
- Target range
- 700 – 1,050 lb 10–15% of 7,000 lb
- Tongue weight needed
- 100 lb To reach the minimum of 700 lb
- How to fix it
- Move 100 lb forward by 16.0 ft Or any equivalent — 200 lb moved half as far does the same. Based on a 16 ft coupler-to-axle span.
- Weight on the trailer axles
- 6,400 lb The remainder. Compare against the trailer’s axle rating, not just the GVWR.
The physics of sway
Trailer sway is a self-reinforcing oscillation, and understanding why it builds explains why tongue weight is the control for it.
A trailer pivots about its hitch ball. If its centre of mass sits well ahead of its axles, any yaw disturbance produces a restoring force that pulls it back into line — the trailer is stable in the same way an arrow with its weight forward flies straight.
Move the centre of mass back toward or behind the axles and that restoring force weakens or reverses. Now a disturbance — a gust, a passing truck, a steering correction — starts an oscillation that feeds energy back into itself with each cycle. Speed makes it worse because the aerodynamic and inertial forces driving it rise with the square of velocity.
Tongue weight is simply a measure of how far forward the centre of mass sits. Ten percent means the mass is comfortably ahead of the axles. Five percent means it is close to them, and the trailer has almost no natural tendency to straighten itself.
Once sway begins at highway speed, braking the tow vehicle transfers weight forward and can make it worse. The recovery is to apply the trailer brakes alone using the controller’s manual lever, which pulls the trailer straight from behind, and to ease off the throttle without steering corrections.
Measuring it without a dedicated scale
A tongue weight scale is the easy answer, but there are two workable alternatives.
The public scale method uses subtraction. Weigh the whole rig with the trailer coupled and note the tow vehicle axle weights. Uncouple, support the trailer on its jack, and weigh the tow vehicle alone. The difference in the rear axle reading is the tongue weight, and it needs no special equipment beyond a few dollars at a CAT scale.
The lever method works at home. Rest the coupler on a bathroom scale through a short length of pipe and a longer beam pivoting on a block, with a known ratio between the distances. The scale reads a fraction of the true weight, multiplied back by the lever ratio. It is fiddly but accurate enough, and it works for tongue weights well beyond the scale’s own capacity.
Whichever you use, measure loaded and ready to travel. Tongue weight changes substantially with where cargo sits, and a trailer measured empty tells you nothing about the trailer you will actually tow.
Loading to hit the target
Tongue weight is not a property of the trailer, it is a property of how you loaded it. The same trailer can measure eight percent or eighteen depending on where the heavy items sit.
The general principle is heavy items forward of the axles and low. Water tanks, batteries, tools and generators are the usual candidates, and moving one of them a few feet changes tongue weight noticeably — which is what the shift figure in the result is calculating.
Loading behind the axles is disproportionately harmful. Cargo aft of the axle line reduces tongue weight and, because it sits far from the pivot, contributes strongly to the yaw inertia that drives sway. A heavy item on the rear bumper of a travel trailer is close to the worst place it can be.
Repeatability matters as much as the number. If you find a loading arrangement that measures in range, photograph it. Trailers get unpacked and repacked, and the arrangement that produced a good measurement is easy to lose.
What this is based on
- Conventional hitch tongue weight convention of 10–15% of loaded trailer weight
- Fifth wheel and gooseneck pin weight convention of 15–25%
- Static moment balance about the trailer axle for the cargo shift calculation
An estimate based on the weights you enter. The cargo shift assumes a single axle group and level ground. Always verify against a scale, and check the tow vehicle’s payload and rear axle ratings separately.
Frequently asked questions
Why does low tongue weight cause sway?
With too little weight on the hitch the trailer’s centre of mass sits close to or behind its axles, so a small disturbance sets up an oscillation the tow vehicle cannot damp. Once it builds at speed, braking the tow vehicle usually makes it worse — trailer brakes alone are the recovery.
How do I actually measure tongue weight?
A dedicated tongue weight scale is easiest. Otherwise a public scale gives it by difference: weigh the whole rig, then weigh again with the trailer uncoupled and supported on its jack. The change in the tow vehicle’s reading is the tongue weight.
Is too much tongue weight also a problem?
Yes. It overloads the rear axle, lifts weight off the front axle and lightens the steering, which reduces braking and cornering control. It also eats payload capacity you may need elsewhere.
Why is the fifth wheel range higher?
A fifth wheel or gooseneck pin sits over or ahead of the rear axle rather than behind the bumper, so the load is carried far more favourably. The geometry tolerates and benefits from a higher share of the trailer weight, typically 15 to 25%.
Does moving cargo forward always help?
It increases tongue weight, which helps if you are light and hurts if you are already heavy. The shift figure here comes from the moment balance about the trailer axle, so it works in both directions.