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Axle weight calculator

Start from what each axle weighs on a scale. Place loads along the truck, in the bed, on the hitch behind the rear axle or on a plow in front, and see how the weight moves between the axles.

Truck

Wheelbase

Center of the front axle to center of the rear axle.Enter a distance.

Front axle weight

From a scale, before the loads below.Enter a weight.

Rear axle weight

From a scale, before the loads below.Enter a weight.

Front GAWR

Gross axle weight rating, on the driver's door jamb label.Enter a weight.

Rear GAWR

Gross axle weight rating, on the driver's door jamb label.Enter a weight.

Loads

Distance is measured from the center of the front axle, toward the rear. A hitch ball sits behind the rear axle, so its distance is the wheelbase plus the overhang. A load ahead of the front axle, like a plow, has a negative distance.

Add

Side view

This is static arithmetic on the numbers you entered, with the truck standing level. It does not say a load is safe or legal. A weight distribution hitch moves some load back to the front axle in a way this cannot predict, so weigh each axle on a scale with the rig hitched. Your GAWR, GVWR and payload are on the door jamb labels.

Why position matters

A load is not carried only by the axle it sits over. It is shared between the two axles by the lever rule: the closer a load is to an axle, the more of it that axle carries. A load behind the rear axle, like tongue weight on a hitch, puts more than its own weight on the rear axle and lifts some weight off the front axle. A plow ahead of the front axle does the opposite.

How it is calculated

For each load of weight P at a distance x behind the front axle, on a wheelbase L, taking moments about the front axle:

rear axle change  = P × x ÷ L
front axle change = P − P × x ÷ L

The changes are added to the axle weights you weighed. The total always goes up by exactly the weight added. Distances can be in inches or centimeters; only the ratio x ÷ L matters.

Worked example

A truck with a 145 inch wheelbase weighs 3,600 lb on the front axle and 2,600 lb on the rear.

600 lb in the bed, 120 inches behind the front axle: the rear axle takes 600 × 120 ÷ 145 = 497 lb and the front takes 103 lb.
900 lb of tongue weight on a ball 190 inches behind the front axle (45 inches behind the rear axle): the rear axle takes 900 × 190 ÷ 145 = 1,179 lb and the front loses 279 lb.

Loaded, the front axle weighs 3,424 lb (176 lb less, 4.9% lighter) and the rear axle 4,276 lb (1,676 lb more). The total is 7,700 lb, exactly the 6,200 lb truck plus 1,500 lb added.

What to compare with

Each axle has a gross axle weight rating (GAWR) on the certification label on the driver's door jamb. Enter them to see each axle as a share of its rating. The truck as a whole also has a GVWR and a payload figure; the payload calculator covers those. The calculation assumes a rigid frame on level ground and no weight distribution hitch.

Questions

How do you calculate axle weight?

Share each load between the axles by its position: the rear axle takes weight × distance from the front axle ÷ wheelbase, the front axle takes the rest. 600 lb at 120 inches on a 145 inch wheelbase puts 497 lb on the rear axle and 103 lb on the front.

Why does tongue weight put more than its weight on the rear axle?

The hitch ball is behind the rear axle, so the tongue weight levers the front of the truck up. 1,000 lb at 190 inches on a 145 inch wheelbase adds 1,310 lb to the rear axle and takes 310 lb off the front.

How much weight does a plow put on the front axle?

More than the plow weighs. A 700 lb plow 40 inches ahead of the front axle on a 145 inch wheelbase adds 893 lb to the front axle and takes 193 lb off the rear.

Where do I find my GAWR?

On the certification label on the driver's door jamb, one figure for the front axle and one for the rear.