Heavy-Duty Towing & Payload Calculator

Works out the maximum trailer weight your truck can carry within its payload rating, given curb weight, GVWR, what is already in the truck, and the tongue or pin weight percentage. Payload is usually the binding constraint rather than the advertised tow rating, which is why trucks are routinely overloaded by owners who checked the wrong number.

How to use it

1. Enter the truck GVWR and curb weight from the door jamb sticker.
2. Enter the weight of passengers and cargo in the truck.
3. Enter the tongue or pin weight percentage — 15 for a bumper pull, 20 to 25 for a fifth wheel or gooseneck.
4. Read the maximum safe trailer weight and remaining payload.

Payload, not tow rating, is the limit

The advertised maximum tow rating assumes a truck with nothing in it beyond a driver, and that assumption almost never holds.

Payload is GVWR minus curb weight — everything the truck can carry, including passengers, cargo, fuel beyond the base figure, aftermarket accessories, the hitch itself, and the tongue or pin weight of the trailer. That last item is the one that consumes payload fastest.

A worked case. A truck with a 7,000 pound GVWR and 5,800 pound curb weight has 1,200 pounds of payload. Two adults and gear at 400 pounds leaves 800. A conventional trailer transfers about 12 to 15 percent of its weight to the hitch, so at 15 percent the maximum trailer is around 5,300 pounds — even if the truck is rated to tow 9,000.

This gap is why half-ton trucks towing large travel trailers are frequently over their payload rating while apparently well within their tow rating. The tow figure is a marketing number; the payload sticker on the door jamb is the legal one, and it is specific to that vehicle as built.

Tongue weight and hitch type

Tongue weight is the downward force the trailer applies at the coupling, and both the percentage and where it acts on the truck depend on the hitch type.

A conventional bumper-pull trailer should carry 10 to 15 percent of its gross weight on the tongue. Below about 10 percent the trailer becomes prone to sway, which is genuinely dangerous and can build into an uncontrollable oscillation. Above 15 percent the rear of the tow vehicle is overloaded and the front unloads, degrading steering and braking.

A fifth wheel or gooseneck carries 15 to 25 percent on the pin, typically around 20. That is a much larger absolute load, but it acts over or ahead of the rear axle rather than behind it, which is why these arrangements are stable at far higher trailer weights. The trade-off is payload: a 15,000 pound gooseneck puts about 3,000 pounds in the bed, which exceeds the entire payload rating of many light-duty trucks.

Weight distribution hitches redistribute tongue load forward via spring bars, restoring front axle load and improving steering. They do not increase payload — the weight is still on the truck — and they are generally required above roughly 5,000 pounds of trailer or 500 pounds of tongue weight.

The other ratings that apply

Payload is the usual constraint but not the only one, and every applicable limit must be satisfied independently.

• GVWR, the maximum loaded weight of the tow vehicle alone including tongue weight.
• GAWR, front and rear axle ratings. It is entirely possible to be under GVWR and over the rear axle rating, particularly with a gooseneck or a heavy bed load.
• GCWR, the maximum combined weight of truck and trailer together. This is what actually limits large combinations, and it is where engine, transmission, and cooling capacity are reflected.
• Maximum tongue weight for the hitch and receiver, which is a separate rating from the truck and is often the lower of the two.
• Tyre load ratings, which are per tyre and can be exceeded even within axle limits if load is unevenly distributed.
• Trailer GVWR and trailer axle ratings, which limit what you can load into the trailer regardless of the truck.

Weighing rather than estimating

Published curb weights are for a base configuration. Real trucks carry aftermarket bumpers, toolboxes, bed liners, tonneau covers, larger tyres, and fuel, and each addition reduces payload by its own weight. A truck with several hundred pounds of accessories has several hundred pounds less payload than the brochure implies, and the door sticker reflects the vehicle as it left the factory rather than as it stands.

A CAT scale visit costs little and gives real figures. Weigh the truck loaded as you would tow it, then weigh the combination hitched. Steer axle, drive axle, and trailer axle weights come out separately, which lets you check every rating rather than only the total, and it will usually reveal that one axle is closer to its limit than expected.

Trailer weights are worth the same scepticism. Dry weight excludes water, propane, batteries, and everything you put inside. Fresh water alone at 8.34 pounds per gallon adds several hundred pounds on a mid-size trailer, and a loaded travel trailer commonly runs 1,000 to 1,500 pounds above its advertised dry weight.

At a glance

Frequently asked questions

Read more

Engineering and vehicle math — Squared and cubed relationships explain most of it: heat, scaling, and why your truck runs out of payload before tow rating.

Related calculators