TowingMath

Towing Capacity Calculator

The brochure number assumes an empty truck. This works out what you can tow with your truck loaded the way you actually drive it.

Your numbers

Gross combination weight rating, from your owner's manual or towing guide.
Empty weight with fluids. Best figure is an actual scale reading.
If entered, the lower of the two limits is used.
Maximum trailer weight —

Enter your numbers above.

Verify before you tow. These figures are a planning aid, not professional or engineering advice. Your real limits are the ones printed on your vehicle's door-jamb placard, your trailer's VIN plate, and your owner's manual - and those override anything calculated here. When numbers are close, weigh the rig and go with the more conservative answer.

The formula

Loaded tow vehicle weight = curb weight + passengers + cargo

Max trailer weight = GCWR - loaded tow vehicle weight

Then take the LOWER of that result and the manufacturer's
advertised maximum tow rating. Both limits apply; neither
overrides the other.

Worked example

A truck with a 17,000 lb GCWR, 5,600 lb curb weight, advertised to tow 11,000 lb. Two adults and a child aboard, 250 lb of gear: 

Loaded tow vehicle = 5,600 + 450 + 250 = 6,300 lb

Max trailer = 17,000 - 6,300 = 10,700 lb

Advertised max tow rating          = 11,000 lb
GCWR-derived limit                 = 10,700 lb
Governing limit (the lower)        = 10,700 lb

So 10,700 lb, not 11,000. And this is still only the tow limit - payload will almost certainly bite first, because a 10,700 lb trailer puts well over 1,000 lb of tongue weight onto a truck that has already spent 700 lb of payload on people and gear.

Run the payload number before you trust this one. For half-ton trucks and travel trailers, payload is the real constraint far more often than tow rating is. Payload capacity calculator.

Common questions

How do I calculate my real towing capacity?

Subtract your tow vehicle's actual loaded weight from its GCWR (gross combination weight rating). What remains is the heaviest trailer the combination can legally carry.

The key word is actual. Not curb weight from a brochure - the weight of the truck as it sits with you, your passengers, your gear and a full tank of fuel. That number is almost always higher than people assume, and every pound of it comes off what you can tow.

Why is my calculated capacity lower than the advertised tow rating?

Because the advertised rating assumes a nearly empty truck. Manufacturers establish maximum tow ratings under SAE J2807 with a defined light load - typically the driver and a small allowance, not a family and a loaded bed.

Load four people and gear into the truck and you have added several hundred pounds that must come out of the GCWR budget. The tow rating did not change, but what you can actually pull did.

What is GCWR?

Gross combination weight rating: the manufacturer-specified maximum for the tow vehicle and trailer together, fully loaded, as a single system. It is defined in federal regulation as "the value specified by the manufacturer as the loaded weight of a combination vehicle".

GCWR is the ceiling that governs the whole rig. Staying under it while being over GVWR or a GAWR is still overloaded - all the limits apply at once.

Is tow rating the limit that actually stops me?

Usually not. For most half-ton trucks pulling travel trailers, payload runs out well before tow capacity does, because tongue weight lands entirely on the tow vehicle.

Work the payload number before you shop for a trailer. A truck rated to tow 11,000 lb may be genuinely limited to a 6,000 lb trailer once the family is aboard.

Related tools

Sources