TowingMath

Tongue Weight Calculator

Enter your loaded trailer weight to get the tongue weight range you should be aiming for. Add a measured tongue weight and it will tell you whether you are inside it.

Your numbers

The trailer as it will actually travel - cargo, water and fuel included.
Leave blank if you have not weighed it yet.
Target tongue 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

Tongue weight is simply a percentage of the trailer's loaded weight. The whole calculation is one multiplication in each direction: 

Target tongue weight = Loaded trailer weight x Target percentage

Conventional / bumper pull:  10% to 15%
Fifth wheel / gooseneck:     15% to 25%

Going the other way, from a measured weight:

Actual percentage = (Measured tongue weight / Loaded trailer weight) x 100

Worked example

A travel trailer weighs 6,000 lb loaded, on a conventional ball hitch. The target range is 10% to 15% of 6,000: 

Low end:   6,000 x 0.10 = 600 lb
High end:  6,000 x 0.15 = 900 lb
Midpoint:  6,000 x 0.125 = 750 lb

Measured on a tongue scale: 540 lb
Actual percentage = (540 / 6,000) x 100 = 9.0%

9.0% is below the range, so this trailer is a sway risk. The fix is to shift cargo forward of the axles until the tongue reads at least 600 lb - not to add weight to the tongue itself, which would raise total weight as well.

Why 10 to 15 percent

The range is not arbitrary, and the two ends fail in opposite directions. Below it, the trailer's center of gravity sits too far rearward and the trailer becomes unstable - NHTSA names insufficient tongue weight as a cause of sway. Above it, the tongue levers weight off the tow vehicle's front axle, costing steering and braking authority, and consumes payload that you may need for passengers and gear.

The 10% floor is worth taking seriously for a specific reason: SAE J2807, the standard manufacturers use to certify tow ratings, assumes 10% tongue weight. Your vehicle's tow rating was established on that assumption. Towing below 10% means operating outside the conditions the rating was tested under.

Tongue weight comes out of payload, not tow capacity. A 900 lb tongue is 900 lb off your truck's payload allowance, before passengers. This is the single most common way a rig that looks fine on paper is actually overloaded - check payload separately.

Common questions

How much should tongue weight be?

For a conventional bumper-pull trailer, aim for 10% to 15% of the trailer's fully loaded weight. SAE J2807, the standard vehicle manufacturers use to establish tow ratings, assumes 10% - so 10% is the floor the rating itself was built on, not a target to dip below.

Fifth-wheel and gooseneck trailers are different: those carry 15% to 25% of loaded weight on the pin, because the load sits over the rear axle rather than behind it.

What happens if tongue weight is too low?

The trailer sways. With too little weight on the tongue, the trailer's center of gravity sits too far back and any disturbance - a crosswind, a passing truck, a lane change - starts an oscillation that grows instead of damping out. NHTSA identifies too little tongue weight as a direct cause of sway.

Sway from low tongue weight is not something you can steer out of reliably. The fix is to move cargo forward, not to drive more carefully.

What happens if tongue weight is too high?

Too much tongue weight pushes down behind the tow vehicle's rear axle, which levers weight off the front wheels. That costs you steering and braking authority at the front, squats the rear, and can overload the rear axle's GAWR even when you are under the tow rating.

It also eats payload directly: every pound of tongue weight is a pound out of your truck's payload allowance.

Do I use loaded or empty trailer weight?

Loaded, always - the trailer as it will actually travel, with water, gear, fuel and cargo aboard. Tongue weight percentage is meaningful only against the weight the trailer really is on the road.

This matters more than it sounds. Loading a heavy item behind the axles can drop a properly balanced trailer below 10% without changing the total weight much at all.

How do I measure actual tongue weight?

A dedicated tongue weight scale is the simplest way, and hitch-mounted scales read it directly. A CAT scale also works: weigh the tow vehicle alone, then weigh it again coupled to the loaded trailer, and the increase on the tow vehicle's axles is your tongue weight.

A bathroom scale works for lighter trailers using a beam-and-pivot arrangement, but the arithmetic is easy to get wrong and the numbers matter, so a purpose-made scale is worth it.

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