How to Measure Tongue Weight: Worked Example With Stated Ratings

How to Measure Tongue Weight is the part of towing maths most people skip, and the part that causes the most trouble when it is wrong. Tongue weight is the downward force the trailer puts on the tow hitch, and the working rule is 10 to 15 percent of the trailer's loaded weight. Too little and the trailer sways; too much and the tow vehicle's steering goes light and its rear suspension bottoms out. This page shows the formula, works through examples at several trailer weights, and explains how to measure it with a scale.

Never exceed your vehicle's GVWR, GCWR or payload. Check the owner's manual and the door-jamb sticker for the ratings that apply to your exact vehicle, and treat every figure on this page as a worked example unless it comes from your own vehicle's plates.

how to measure tongue weight: The method: the lowest of three ratings

Three ratings decide what you may tow, and the answer is the smallest of them: the vehicle's tow rating, the tow-bar rating and the trailer's ATM — the aggregate trailer mass, the most the loaded trailer is rated to weigh. Here the worked example uses 9,000 lbs for the vehicle, 4,000 lbs for the tow bar and 5,500 lbs for the trailer ATM, which makes the towing capacity 4,000 lbs. Those numbers are examples, not ratings for any real vehicle: read the three figures off your own manual and plates and the same step gives your answer. Each rating guards a different part of the rig — the vehicle's engine, transmission, brakes and cooling; the tow bar and its mounting; the trailer's axles, tyres and brakes — so the weakest link sets the limit. That is the point this page works through for how to measure tongue weight.

There is a second layer of limits behind the tow rating. The loaded vehicle may not exceed its GVWR, the vehicle-plus-trailer combination may not exceed its GCWR, and the payload — the gap between kerb weight and GVWR — has to cover passengers, cargo and the tongue weight of the trailer. That last point is the one people miss: the hitch load is carried by the vehicle, so a heavy trailer shrinks the payload left for everything else. Pass the tow-rating check and still fail GCWR or payload, and the combination is overloaded. Check all three against the figures for your exact vehicle in the manual and on the door-jamb sticker.

how to measure tongue weight: Where to find your ratings

Start with the owner's manual: it lists the tow rating by engine, axle ratio and configuration, and it states the GVWR and GCWR. Then check the door-jamb sticker on the driver's door, which gives the GVWR and the payload for your exact vehicle as built — this is the number that matters, because options fitted at the factory change it. The tow bar itself has a rating plate, usually stamped on the bar or on a label near the receiver, and the trailer has a compliance plate showing its ATM and its tare (empty) weight. If the manual and the sticker disagree, use the lower figure and ask a dealer to confirm for your VIN. Never take a rating from a forum, a sales listing or a figure quoted for a different year or engine: ratings change with engine, axle ratio, cab, bed length and tow package, and the only numbers that count are the ones for your vehicle.

Tongue weight: the 10 to 15 percent rule for how to measure tongue weight

Tongue weight should be 10 to 15 percent of the trailer's loaded weight. For a 4,500 lbs trailer that is 450 to 675 lbs, with about 562 lbs as a good middle target. Below 10 percent the trailer is prone to sway, because there is not enough downward force on the hitch to keep it tracking straight; above 15 percent the tow vehicle's rear suspension is overloaded, the steering goes light and the headlights point at the sky. The fix for wrong tongue weight is loading, not guessing: move heavy items forward of the trailer axle to increase it, or behind the axle to reduce it, and re-weigh. Never fix sway by adding speed — slow down, and check the loading before the next trip.

how to measure tongue weight: How to measure tongue weight

Taking how to measure tongue weight as the case in point: The accurate way is a tongue-weight scale under the coupler with the trailer level and loaded as it will travel. A bathroom scale and a lever can work for lighter trailers, but the reading is only as good as the setup, so a proper scale is worth it for anything heavy. Measure with the trailer loaded as it will travel — water tanks, gas bottles, luggage and all — because an empty trailer tells you nothing about the loaded figure. Record the number, divide it by the trailer's loaded weight, and check the percentage is inside 10 to 15 percent. If it is not, reload and measure again.

Worked example: the three ratings and the payload check for how to measure tongue weight

Take a 4,500 lbs loaded trailer as the example. The vehicle's tow rating is 9,000 lbs, the tow-bar rating is 4,000 lbs and the trailer ATM is 5,500 lbs. The towing capacity is the lowest of the three: 4,000 lbs. The trailer's tongue weight at 10 to 15 percent is 450 to 675 lbs, and the middle of that range — about 562 lbs — is a good target. With an example payload of 1,600 lbs, the tongue weight leaves 1,038 lbs for passengers and cargo. If the passengers and luggage weigh more than that, the combination is overloaded even though the trailer is inside the tow rating, and something has to come off — either the trailer load or the vehicle load. That is the whole check in one paragraph: lowest of three, then tongue weight, then payload, then GCWR. Do it with your own numbers before every trip, because the answer changes every time the load changes.

how to measure tongue weight: Tongue weight table

On this page, how to measure tongue weight is the case in point: The tongue-weight range below is 10 to 15 percent of the loaded trailer weight, with 12.5 percent in the middle as a practical target. Find your trailer's loaded weight in the first column and read across. Weigh the trailer as it will travel — guessing the weight makes the whole table useless.

Loaded trailer weight (lbs) 10% tongue weight 12.5% tongue weight 15% tongue weight
3,500 350 438 525
5,000 500 625 750
6,000 600 750 900
7,000 700 875 1,050
10,000 1,000 1,250 1,500

The four checks, in order for how to measure tongue weight

Check What to compare Passes when
Tow rating Trailer weight vs lowest of vehicle, tow-bar and trailer ATM ratings Trailer weight is at or below the lowest rating
Tongue weight Tongue weight against 10–15% of trailer weight Percentage sits inside 10–15%
Payload Tongue weight plus passengers and cargo against payload Sum is at or below payload
GCWR Vehicle + trailer loaded weights vs GCWR Combined weight is at or below GCWR

Common mistakes for how to measure tongue weight

  • On this page, how to measure tongue weight is the case in point: Loading the trailer tail-heavy to reduce tongue weight. Putting weight behind the axle lightens the hitch, but it is the fastest way to make a trailer sway, and sway at speed is far more dangerous than a heavy hitch.
  • Taking how to measure tongue weight as the case in point: Ignoring the GCWR. A combination can be inside the tow rating and still over the GCWR once the vehicle is fully loaded with people and luggage.
  • Using the trailer's empty weight instead of its loaded weight. A trailer's tare weight is the empty figure; the loaded weight is what the ratings are tested against, and water, gas, luggage and equipment can add hundreds of pounds. That is the point this page works through for how to measure tongue weight.
  • Taking how to measure tongue weight as the case in point: Guessing the trailer's weight instead of weighing it. Bathroom scales and guesswork are not a substitute for a weighbridge or a proper scale, and an overloaded trailer is the most common cause of towing trouble.

Related calculations for how to measure tongue weight

On this page, how to measure tongue weight is the case in point: If this page answered your question, these pages take the next step — the same method applied to a closely related question, or the calculator that does the arithmetic for you.

how to measure tongue weight: Putting your figure to work

The check only helps if you run it on your own numbers every time the load changes. Weigh the trailer as it will travel, take the three ratings from your manual and plates, work out the tongue weight and check payload and GCWR. Keep the four answers with the trailer's paperwork — lowest rating, tongue-weight range, payload left over, GCWR headroom — and redo them when anything changes: a full tank, another passenger, a different trailer. Loads change, so the answer changes, and the habit of re-checking is what keeps the combination legal and stable. That is the point this page works through for how to measure tongue weight.

Frequently asked questions

What is GVWR and what is GCWR?

GVWR is the maximum weight of the loaded vehicle on its own. GCWR is the maximum weight of the vehicle and the trailer together. Both have to be respected: the tow rating alone is not enough, because a fully loaded vehicle plus a heavy trailer can exceed the GCWR even when the trailer is inside the tow rating.

Do I need trailer brakes?

On this page, how to measure tongue weight is the case in point: That depends on the trailer's weight and local rules: heavier trailers generally require their own brakes, and the threshold varies by country and by state. Check the trailer's ATM, the tow vehicle's manual and the local regulations. A trailer with brakes stops shorter and puts less load on the tow vehicle's brakes, which is why the braking requirement exists.

Is it safe to tow at maximum capacity?

The rating is a maximum under the manufacturer's test conditions, not a target. Most experienced towers leave a margin — aiming to tow at 80 percent or less of the rated capacity as a rule of thumb — so that hills, wind and a fully loaded trailer do not push the combination to its limit. Always check GVWR, GCWR and payload as well as the tow rating.

Why does my trailer sway?

Sway usually means the tongue weight is too low, the load is tail-heavy, or the speed is too high for the combination. Slow down smoothly without braking hard, and check the loading before the next trip — moving weight forward of the trailer axle is the usual fix. That is the point this page works through for how to measure tongue weight.

What is trailer ATM?

Taking how to measure tongue weight as the case in point: ATM is the aggregate trailer mass: the maximum the trailer is allowed to weigh when fully loaded, set by the trailer manufacturer. It is on the trailer's compliance plate, and it is one of the three ratings in the lowest-of-three rule — your towing capacity can never exceed the trailer's ATM.