How to Calculate Tongue Weight: How the Lowest-of-Three Rule Works

How to Calculate 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.

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

Towing capacity is the lowest of three numbers: the vehicle's tow rating, the tow-bar rating and the trailer's ATM (aggregate trailer mass — the maximum the trailer itself is rated to weigh when loaded). If any one of them is lower than the others, that one is the limit. In this page's worked example the three ratings are 11,000 lbs for the vehicle, 7,500 lbs for the tow bar and 4,500 lbs for the trailer ATM, so the towing capacity is 4,500 lbs — the lowest of the three. Those are example figures, not ratings for any particular vehicle: substitute the three numbers from your own owner's manual, tow-bar plate and trailer plate and the same step gives your answer. The reason the rule exists is that each rating protects a different part of the combination — the vehicle's engine, transmission, brakes and cooling; the tow bar and its mounting; and the trailer's axles, tyres and brakes — and the weakest of the three decides what is safe to pull.

The tow rating alone is not the whole answer. GVWR caps the loaded vehicle, GCWR caps the vehicle and trailer together, and payload — GVWR minus kerb weight — caps what the vehicle itself may carry, including the tongue weight pressing down on the hitch. A heavy trailer therefore eats into the passengers and cargo you can carry, and a combination can be inside the tow rating yet still overloaded on GCWR or payload. Every limit has to pass at once, and the numbers for your exact vehicle are in the owner's manual and on the door-jamb sticker.

Where to find your ratings for how to calculate tongue weight

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 calculate tongue weight

Taking how to calculate tongue weight as the case in point: Tongue weight should be 10 to 15 percent of the trailer's loaded weight. For a 5,000 lbs trailer that is 500 to 750 lbs, with about 625 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 calculate tongue weight: How to measure tongue weight

On this page, how to calculate tongue weight is 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.

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

Take a 5,000 lbs loaded trailer as the example. The vehicle's tow rating is 11,000 lbs, the tow-bar rating is 7,500 lbs and the trailer ATM is 4,500 lbs. The towing capacity is the lowest of the three: 4,500 lbs. The trailer's tongue weight at 10 to 15 percent is 500 to 750 lbs, and the middle of that range — about 625 lbs — is a good target. With an example payload of 1,600 lbs, the tongue weight leaves 975 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 calculate tongue weight: Tongue weight table

For how to calculate tongue weight, the point is this: Use the table to read off the tongue-weight range for your loaded trailer weight. The middle column, 12.5 percent, is a handy loading target. Every figure is worked out from the trailer weight, so weigh the loaded trailer rather than guessing it.

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 calculate 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 vs 10–15% of trailer weight Inside the range
Payload Tongue weight + passengers + cargo vs payload Total is at or below payload
GCWR Vehicle + trailer loaded weights vs GCWR Combined weight is at or below GCWR

how to calculate tongue weight: Common mistakes

  • Taking how to calculate tongue weight as the case in point: Skipping the brake check on the trailer. A trailer's brakes need testing before every trip, not just at service time — a seized or disconnected trailer brake puts the whole stopping job on the tow vehicle.
  • Taking how to calculate tongue weight as 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.
  • For how to calculate tongue weight, the point is this: Trusting a figure quoted for a different year, engine or configuration. Tow ratings change with engine, axle ratio, cab and tow package, so only the numbers for your exact vehicle count.
  • Taking how to calculate tongue weight as the case in point: Hitching up without checking the coupler is locked. A coupler that looks seated but is not latched can come off on the first bump, and the safety chains are a last resort, not a towing method.

Related calculations for how to calculate tongue weight

These pages continue from here: the same method on a neighbouring question, or the calculator that runs the arithmetic for you. That is the point this page works through for how to calculate tongue weight.

Putting your figure to work for how to calculate tongue weight

For how to calculate tongue weight, the point is this: Use the method as a pre-trip routine. Before you hitch up, weigh the loaded trailer, confirm the three ratings from your own documents, calculate the tongue weight and check it against payload and GCWR. Note the four results and keep them with the trailer's documents. Any change in load — water, luggage, passengers, a different trailer — means a fresh check, because the numbers move with the load. Done every trip, the routine takes minutes and keeps the combination inside its limits where it matters: on the road.

Frequently asked questions

How do I work out my towing capacity?

Take the lowest of three ratings: your vehicle's tow rating, your tow-bar rating and the trailer's ATM. Then check the tongue weight is 10 to 15 percent of the trailer weight, and check the combination against GVWR, GCWR and payload. All four checks have to pass. The ratings come from your owner's manual, the door-jamb sticker, the tow-bar plate and the trailer plate — not from a figure quoted for a different vehicle.

Do I need a special licence to tow?

It depends on where you are and how heavy the combination is. Licence categories limit the combined weight you may tow, and the rules differ by country. Check your licence entitlement before towing, not after you are stopped. That is the point this page works through for how to calculate tongue weight.

What is trailer ATM?

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. That is the point this page works through for how to calculate tongue weight.

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 calculate tongue weight.

What is noseweight for a caravan?

For how to calculate tongue weight, the point is this: Noseweight is the UK term for the downward force a caravan puts on the tow ball — the same thing as tongue weight. The commonly quoted guideline for caravans is 5 to 7 percent of the caravan's loaded weight, lower than the 10 to 15 percent used for other trailers, because caravans are designed around it.