Trailer Tongue Weight Calculator

What tongue weight is, and why it matters

Tongue weight — tow-ball weight or ball weight in the UK and Australia — is the downward force the front of the trailer presses onto the hitch ball. It is the single most important number for towing stability. Too little and the trailer’s centre of gravity drifts toward or behind its axle, so a bump or gust can set it pivoting and the tail of the tow vehicle starts to wag: that is sway, and it gets worse with speed. Too much and the hitch shoves the rear of the truck down, lifting the front wheels and robbing steering and braking grip. The job is to land in the band that keeps the trailer’s weight ahead of its axle without overloading the back of the truck.

The target: what your tongue weight should be

For a conventional bumper-pull (tag) trailer the accepted range is 10 to 15 percent of the gross, fully-loaded trailer weight, and many experienced towers aim for 12 to 13 percent for a margin against sway. Gooseneck and fifth-wheel trailers couple over the rear axle and ride more stably, so their pin weight runs higher, roughly 20 to 25 percent. The table shows the band for common loaded weights.

target tongue weight = gross trailer weight × target %
tongue % = tongue weight ÷ gross trailer weight × 100

How cargo placement controls it — the see-saw

A loaded trailer balances on its axle like a see-saw. Weight placed ahead of the axle presses the tongue down; weight behind the axle lifts it. The amount each item contributes is a lever: its weight times how far ahead of the axle it sits, divided by the distance from the coupler to the axle. That is why sliding a heavy item forward a couple of feet can swing tongue weight by a hundred pounds, and why the cure for both too-light and too-heavy tongue weight is almost always moving cargo rather than changing the trailer.

tongue weight from a load = load weight × (distance ahead of axle ÷ coupler-to-axle length)
total tongue weight = empty-trailer tongue weight + the load terms

The standard starting point is the 60/40 rule: put about 60 percent of the cargo weight in the front half of the trailer, ahead of the axle, centred side to side and tied down. That usually lands tongue weight in range — then measure and fine-tune. The load-placement mode above does this arithmetic and draws where the cargo sits relative to the axle.

How to measure tongue weight without a scale

Most travel trailers have more tongue weight than a bathroom scale can take directly, so you borrow a lever to share the load. The trick is mechanical advantage: put the coupler between two supports, and the scale only carries a known fraction of the real weight.

Bathroom-scale and lever method

1. On level ground, lay a strong board (a 2×8 or similar, at least ~3½ ft) flat.
2. Put a brick or block under one end and a bathroom scale under the other, with a piece of plywood protecting the scale. Both supports must be the same height so the board is level.
3. Rest the trailer coupler on a short vertical pipe sitting on the board, between the two supports, at towing height. Lower the jack until the coupler’s full weight is on the board and the jack wheel is off the ground.
4. Read the scale, then multiply by the lever ratio. Place the coupler so it sits closer to the block: for example 1 ft from the block and 2 ft from the scale gives a ratio of 3.

tongue weight = (scale reading − half the board weight) × (total span ÷ block–to–coupler distance)
total span = block–to–coupler + coupler–to–scale

Put plainly: the scale supports the share of the load on its side of the coupler. If the coupler is 1 ft from the block and 2 ft from the scale (a 3 ft span), the scale carries one-third, so multiply the reading by 3. A 200 lb reading is a 600 lb tongue weight. (A common shorthand quotes “2 ft to the scale, 1 ft to the block, ×3” — same thing.) Subtract roughly half the board’s own weight from the reading first for a cleaner figure.

Fulcrum (brick / board) method

For lighter trailers whose tongue weight is under the scale’s own limit (most scales top out around 300–400 lb), skip the lever: stack the bathroom scale on a sturdy block so its top sits at coupler height, lower the coupler directly onto the centre of the scale until the jack wheel lifts off, and read it straight. No multiplication. The board-and-fulcrum lever above is only needed once the tongue weight exceeds what the scale can take by itself.

Whichever method, measure on level ground with the trailer at its normal towing height and loaded exactly as you’ll tow it — tongue weight is a percentage of the loaded weight, so an empty reading tells you little.

Weight-distribution hitches and the rear axle

A weight-distribution hitch does not make the tongue weight smaller — the same force is still there — but it uses spring bars to spread that force onto the tow vehicle’s front axle and back onto the trailer’s axles, instead of dumping it all on the truck’s rear axle. That puts weight back on the front wheels for steering and braking and levels the rig. It is generally recommended once tongue weight gets heavy — often quoted around 350 to 500 lb, or for a trailer more than about half the tow vehicle’s weight. It does not change the fact that the full tongue weight counts against the tow vehicle’s payload.

Federally relevant terms