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Fifth Wheel Weight Calculator

The primary purpose of this calculator is to answer the question: "How heavy a fifth wheel can I tow with my truck?"

This calculator is designed for fifth wheel trailers, towed by a fifth wheel hitch mounted in the bed of a truck above the rear axle.

In the form below, enter as many pieces of inforamtion as you have, and click the Calculate button at the bottom. The more information you provide, the more accurate the calculation will be. The reverse is also true—the less information you provide, the less accurate the results.

If you are unfamiliar with the weights or abbreviations, you may want to start with Understanding RV Weights.

For additional details, please see the scenarios below the calculator.


Item Qty Units Weight (lb)* Weight (kg)*

Tow vehicle GVWR

Enter Gross Vehicle Weight Rating as provided by tow vehicle manufacturer.

lb

kg

Tow vehicle GCWR

Enter Gross Combination Weight Rating as provided by tow vehicle manufacturer.

lb

kg

Tow vehicle maximum loaded trailer weight rating

Enter rating as provided by vehicle manufacturer.

lb

kg

Tow vehicle maximum king pin weight rating

Enter rating as provided by vehicle or hitch manufacturer, whichever is less.

lb

kg

Tow vehicle RGAWR

Enter Rear Gross Axle Weight Rating as provided by tow vehicle manufacturer.

lb

kg

Tow vehicle GVW

Enter actual weight (Gross Vehicle Weight) of tow vehicle.

lb

kg

Tow vehicle RGAW

Enter actual weight of tow vehicle's rear axle (Rear Gross Axle Weight), without trailer attached.

lb

kg

Fifth wheel trailer GVW (or GTW)

Enter actual weight (Gross Vehicle Weight or Gross Trailer Weight) of trailer.

lb

kg

Fifth wheel trailer king pin weight

Enter actual king pin weight of trailer.

lb

kg

Safety margin

Enter a percentage (1 to 50) of the tow vehicle′s maximum ratings you wish to leave as a safety margin. Recommended margin is 20%.

Fifth wheel trailer king pin weight percentage override

Leave this box empty for the calculator to use the recommended 25% maximum as the king pin weight. Enter a percentage (1 to 50) to use as king pin weight instead. Recommended range is 15% - 25%.

Reset Form

* The results of this calculator are approximate. Results may be slightly inaccurate due to conversion and rounding. Weight of liquids vary slightly with temperature, altitude, chemical composition, etc.

Scenario: Maximum trailer weight reduced by GVW

In this scenario you know quite a bit about the truck. You have entered the maximum trailer weight rating, as well as the actual truck weight (GVW) and rear axle weight (RGAW). Since buying the truck, you have installed a heavy toolbox in the bed, increasing the truck weight by almost a 1,000 lbs. Because of this, the calculator found the GVW to be the most restrictive number, and reduced the maximum trailer weight accordingly.

Example, using the 2005 Dodge RAM 1500, regular cab, 4x4, 5.7L HEMI Magnum V8 engine:

  • Tow vehicle GVWR: 6,350 lbs
  • Tow vehicle GCWR: 14,000 lbs
  • Tow vehicle maximum loaded trailer weight rating: 8,900 lbs
  • Tow vehicle RGAWR: 3,900 lbs
  • Tow vehicle GVW: 5,845 lbs
  • Tow vehicle RGAW: 2,921 lbs
  • Calculated Maximum Trailer Weight: 2,020 lbs

As you can see, the calculated result of 2,020 lbs is significantly lower than the maximum specified by Dodge at 8,900 lbs. The large difference is because the manufacturer ratings use the truck weight with standard equipment and driver only. Options and cargo add to the truck weight, reducing towing capacity.

Additionally, the Dodge numbers assume a 15% king pin weight, while the calculator assumes a more restrictive 25%. Enter 15% in the Fifth wheel trailer king pin weight percentage override box and re-calculate, resulting in a higher Maximum Trailer Weight of 3,367 lbs. While the lower percentage makes it look as if you can tow more, you need to find out the actual king pin weight and percentage before settling on this number.

To see how each value affects the calculated maximum trailer weight, try this: Enter the first two values above and click Calculate. Then, enter all additional values, clicking Calculate after each one.

Scenario: Only know the truck's GVWR and GCWR

If you only know the truck's GVWR and GCWR, enter them into the first two boxes. Maximum trailer weight will be calculated by subtracting GVWR form GCWR.

Example, using the 2002 Ford F-350 truck:

  • Tow vehicle GVWR: 11,500 lbs
  • Tow vehicle GCWR: 20,000 lbs
  • Calculated Maximum Trailer Weight: 8,500 lbs

While this result gives you a very rough estimate of the tow vehicles potential, it has the following problems:

  • Calculated trailer weight assumes that the tow vehicle weighs its maximum rating, in this case 11,500 lbs. For better accuracy, enter the tow vehicle's actual weight in the Tow vehicle GVW field.
  • Using only GVWR and GCWR ignores other manufacturer specified weight constraints such as the maximum loaded trailer weight, maximum king pin weight, and RGAWR. For better accuracy, enter as many of these values as possible.

Scenario: Only know the hitch maximum king pin weight rating

If you only know the hitch rating as specified by the manufacturer, enter it in the Tow vehicle maximum king pin weight rating box.

Example, using the 2005 Chevrolet Colorado, crew cab, 2WD, Vortec 2800 I-4 engine:

  • Tow vehicle maximum king pin weight rating: 500 lbs
  • Calculated Maximum Trailer Weight: 2,000 lbs

If the maximum king pin weight used in this calculation is from the hitch manufacturer, this result may be highly inaccurate because the hitch rating may have no relevance whatsoever to the truck ratings. On the other hand, if the maximum king pin weight is from the truck manufacturer for this specific vehicle, then the calculation would be more accurate. In either case, using this number alone is insufficient because of the following:

  • Calculation assumes that king pin weight is 25% of the total trailer weight. Variation in king pin weight percentage will make this assumption invalid.
  • Using only the maximum king pin weight ignores other manufacturer specified weight constraints such as GVWR, GCWR, maximum loaded trailer weight (or GTW) and RGAWR. For better accuracy, enter as many of these values as possible.

The actual maximum trailer weight rating for this vehicle is 1,700/2,900 lbs (manual/auto transmission), as specified by Chevrolet.


These scenarios illustrate that relying on too little information may cause you to exceed manufacturer ratings. On the other hand, providing the calculator with all relevant weight numbers will produce accurate results.