Skip to Main Content

Do the Math on Towing Capacity

By Michael Vatalaro, BoatU.S. Magazine Contributing Writer

Photos by courtesy of BoatU.S.

To determine if your truck or SUV is up to the task of towing your next boat, you’ll need to answer three questions: How much does the truck weigh? How much does the boat and trailer combo weigh? And how much weight can the truck safely accelerate, control, and brake? We’ll assume you have a rough estimate of how much the boat and trailer weigh. You can find the answers to the other two questions on the automaker’s website, or at such sites as Edmunds or Kelley Blue Book, but first it helps to know what numbers to jot down, how to add them up, and what acronyms result from the math.

Curb Weight + Payload = GVWR

The Gross Vehicle Weight Rating (GVWR) of the truck equals the truck’s curb weight (the total weight of the vehicle with standard equipment) plus its payload capacity. Payload capacity tells you how much the people, gear, pets, and everything else in or on the truck can weigh before the truck is overloaded. For trailering purposes, tongue weight (the downward weight the trailer exerts on the hitch) counts against the payload. You’re not likely to see GVWR listed on a website, but curb weight and payload are easy to find, particularly for trucks.

Curb Weight + Towing Capacity + 180 = GCWR

The truck’s Gross Combined Weight Rating (GCWR) is the maximum weight the truck can safely get moving—and stop! This number is frequently, but not always, equal to the vehicle’s curb weight plus the towing capacity (how much your rig can pull) and the assumed weight (180 pounds) of the driver. You will sometimes see GCWR listed on the automakers’ sites, but more often, it’s easier to find towing capacity and just do the math.

These numbers are maximums—neither can be exceeded without compromising safety. When the weight of the boat/trailer combo is added to the curb weight of the vehicle, the total must be less than the GCWR or you risk not being able to control the truck/trailer combo on the road. Similarly, if you max out the towing capacity of your truck with a heavily loaded boat and trailer, you’ll have no room in the equation for any passengers or gear in the truck. Experts suggest that the weight of the fully loaded boat/trailer be no more than 85% of the tow capacity to allow a reasonable payload in the truck.

Three “Weighs” To Figure Tongue Weight

Tongue weight is exactly what it says: the weight of the trailer tongue on the hitch of the tow vehicle. The rule of thumb is that you want a tongue weight equal to 7 percent to 12 percent of the total weight of the (fully loaded with fuel and gear) boat/motor/trailer combo. Tandem- and tri-axle boat trailers usually require a percent or two less tongue weight than recommended for a single-axle boat trailer.

If the tongue weight is too low, the boat trailer will sway from side to side when you reach speeds approaching 30 mph. If it’s too high, the trailer will “push” the tow vehicle, making it more difficult to control when braking because so much weight is on the tongue. It’s important to have the trailer as level as possible when attached to the tow vehicle. Too great an angle can affect the trailer’s braking ability.

To measure tongue weight, take the boat, trailer, and tow vehicle fully loaded to a truck scale or a landfill/recycling facility and use one of the following methods. Call ahead and see if they can accommodate you.

>> 1. Pull the truck onto the scale, leaving the trailer hooked up to it, but having the wheels of the trailer off the scale. Get the weight—let’s say it’s 4,600 pounds. Then drive off the scale, disconnect the trailer, and drive the truck back on the scale again and weigh it alone—let’s say the truck weighs 4,200 pounds. The difference (4,600 – 4,200 = 400) is the tongue weight.

>> 2. Drive the truck onto the scale as in Step 1, but instead, disconnect the trailer, leaving just the tongue jack on the scale, but the wheels of the trailer off the scale. Drive the truck off the scale. Get a 4×4 piece of lumber about 17 inches long, place it under the coupler where the ball would normally go, slowly crank the tongue jack until the tongue jack wheel is half an inch off the ground, so the trailer is sitting only on the 4×4 (but don’t remove or swing the tongue jack out of the way in case the trailer falls off the 4×4). Read the scale. That’s your tongue weight weighed right at the coupler, where it should be measured. If you simply use the tongue jack as the weighing point, it skews the tongue weight to the heavy side.

>> 3. Use a tongue weight scale. There are several versions on the market. Check the weight ratings before buying.

A high-tech option

Want to know the real-time live weight of your vehicle and trailer at the touch of a button? The BetterWeigh mobile towing scale plugs into your vehicle’s diagnostic port below the steering wheel. To use, download the BetterWeigh app for iOS and Android, pair the scale with your smartphone, and calibrate using your vehicle’s VIN number.

The weigh feature measures the gross combined weight, which includes the vehicle, cargo, passengers, and trailer. It will also calculate tongue weight, weight distribution, and more. It’s compatible with gas vehicles 1996 and newer and diesel vehicles 2004 or newer.

Want to know the tow capacities of many 2021 SUV and truck models? We’ve got them! Visit for a link to the BoatU.S. vehicle tow capacity list.

Your tow vehicle must have the ability to safely and easily get moving—and stop—with not only the weight of the boat and trailer, but also any gear and passengers.

This article was reprinted with permission from BoatU.S. Magazine, flagship publication of the membership organization Boat Owners Association of The United States (BoatU.S.). For more expert articles and videos to make your boating, sailing, or fishing better, visit


  • January 26, 2022