Weight and density

Every load has two ceilings: space and weight. Which one you hit first depends on the freight. Bottled water, paper, canned food and steel are dense: the truck reaches its weight limit with floor space left over. That's called weighing out. Chips, toilet paper, insulation and empty plastic bottles are light: the trailer fills up long before the weight limit. That's cubing out.

On US Interstate highways the federal limit for a truck's gross vehicle weight is 80,000 lbs: the tractor, the trailer, the fuel, the driver and the freight together. States set limits for their other roads, some allow more with a permit or under older laws, and other countries use different numbers entirely (an EU truck crossing borders is usually limited to 40 tonnes, Canadian provinces mostly allow more on the right axle setup). Always plan to the limit for the roads the load will use.

What's left for freight is the payload: the gross limit minus the tare weight, which is the truck and trailer empty. A typical tractor with fuel and an empty 53-foot dry van weighs about 33,000 to 35,000 lbs, which leaves roughly 45,000 lbs for freight. A reefer, with its insulation and cooling unit, leaves a little less. Check the actual tare for the equipment; a heavy sleeper tractor can cost you a few pallets.

Density is weight per cubic foot: a pallet's weight divided by its cube. Freight much heavier than the trailer's break-even (around 10 to 12 lbs per cubic foot for a dry van) will weigh out; much lighter freight will cube out. It's a quick test before you start fitting pallets.

Order: 26 pallets of canned beans, 1,900 lbs each

Freight      26 x 1,900 = 49,400 lbs
Payload      80,000 - 34,500 tare = 45,500 lbs
Over by      3,900 lbs
Most that fit  45,500 / 1,900 = 23.9  -> 23 pallets

The planner's trick is to mix. Put a weigh-out product and a cube-out product on the same trailer, and you can use both the weight and the space: beans on the floor up front, paper towels stacked on top or behind. Many shippers' load-building software does this, but a planner still needs to see when a load is lopsided, too heavy, or carrying air.