031 Mass and Balance topic guide
Floor Loading: Running and Area Load Limits
Cargo compartments carry two separate load limits, and a pallet or container has to satisfy both at once. Area load spreads a mass over the whole footprint that touches the floor, expressed in kilograms per square metre, and it protects the floor panel and the structure beneath from an evenly distributed weight. Running load, sometimes called linear load, spreads a mass along a single length in the direction the item sits, expressed in kilograms per metre, and it protects against loads that are long and narrow rather than evenly spread over a wide area.
Both figures come from the same starting point, the mass of the item, but they divide by different things: area load divides by the whole footprint area, running load divides by a length. Checking only one of the two limits is not enough, because a load can comfortably clear the area limit while still breaching the running limit, or the other way round, depending on its shape.
Area load and running load compared
A pallet with a wide, roughly square footprint is usually the area-load case: multiply its two side lengths together for the footprint area in square metres, then divide the mass by that area. A wheeled unit, a long crate, or anything that presents a narrow line of contact to the floor is more often the running-load case: divide the mass by the length of that contact in the direction of loading, not by an area at all.
Load spreaders, timber boards or purpose-built spreader plates placed under concentrated legs or wheels, work by increasing the effective contact area without adding meaningful mass. A 300 kg leg resting on a 0.2 m by 0.2 m foot, an area of 0.04 square metres, imposes 300 / 0.04, or 7500 kg per square metre, which would fail almost any floor panel. The same 300 kg spread across a 1.0 m by 0.5 m spreader board, an area of 0.5 square metres, imposes only 300 / 0.5, or 600 kg per square metre, a realistic pass.
Checking a load against the placarded limits
The working method is always the same: compute the actual figure, area load or running load, as the load's shape demands, and compare it to the compartment's placarded limit for that same figure. A running-load check on a 1750 kg container with a 2.5 m contact length in the load direction gives 1750 / 2.5, or 700 kg per metre; if the compartment placard reads 800 kg per metre, the load complies, with 100 kg per metre of margin.
The exam usually gives a mass and one or two dimensions and expects you to recognise which limit applies before doing the division. Reaching for the wrong denominator, a single side length instead of the full footprint area, or the full footprint area when only a length was wanted, produces an answer that looks clean but checks the wrong thing entirely.
Worked example
Worked example: checking a pallet against a floor limit
Not quite. The correct answer is A.
Correct answer: A
- A. Correct: footprint area is 1.5 x 2.0 = 3.0 square metres, and 1050 / 3.0 = 350 kg per square metre, which is below the 400 kg per square metre limit.
- B. This divides the mass by the 2.0 m side alone (1050 / 2.0 = 525), treating one side of the footprint as if it were the whole area.
- C. This divides the mass by the 1.5 m side alone (1050 / 1.5 = 700), the same single-dimension error as option B, using the other side.
- D. This multiplies the mass by the footprint area instead of dividing by it (1050 x 3.0 = 3150), inverting the whole calculation.
Step by step
- Find the footprint area: 1.5 m x 2.0 m = 3.0 square metres.
- Divide the pallet's mass by that area: 1050 kg / 3.0 square metres = 350 kg per square metre.
- Compare to the placarded limit: 350 kg per square metre is below the 400 kg per square metre limit, so the pallet complies, with 50 kg per square metre of margin.
- Sanity check: dividing by the full footprint (3.0 square metres) must give a smaller figure than dividing by either single side alone, and 350 is indeed smaller than both 525 and 700.
Common mistakes
Dividing by a single side length instead of the full footprint area
This produces an area-load figure several times larger than the true one, because it uses only one dimension instead of both, and it can wrongly fail a load that actually complies.
Checking only the limit that is easiest to calculate
Area load and running load are independent checks. A load can pass one and fail the other depending on its shape, so skipping either check risks accepting an overloaded floor.
Forgetting that a spreader increases area, not mass
A spreader board changes only the footprint the load bears on. Using its size to also adjust the mass in the calculation double counts the benefit and understates the true load.
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Last reviewed July 2026