Specific gravity is the number that breaks your racking

The arithmetic, once

Gross weight equals tare plus (gallons × 8.34 lb × specific gravity). That is the whole calculation and it takes ten seconds, but it gets skipped because the tote is treated as the unit rather than the contents.

Eighty percent. That is the spread between the lightest and the heaviest thing routinely shipped in an identical container, and it is invisible from the outside.

Where it bites

Racking

Selective pallet racking is rated per pair of beams, not per position, and a great deal of installed racking in this part of the world is rated somewhere between 4,000 and 6,000 lb per beam pair. Two positions of 3,600 lb caustic is 7,200 lb. That is over rating on a lot of installations, and the failure mode of overloaded racking is not gradual.

Forklifts

Capacity plates are rated at a 24-inch load centre. A 48-inch-deep container puts the centre of gravity around 24 inches out if it is uniformly loaded, which it is — but the derating that matters is at height. A truck rated 5,000 lb at 24 inches and low lift may be rated appreciably less at 150 inches, and that is where the rack beam is.

Stacking

The data plate gives a stacking test load in kilograms. Two-high filled is fine for water. Two-high filled for something at SG 1.5 may exceed the rating of the container below, and HDPE creep accelerates with load and with temperature. On a hot slab, an over-loaded bottom container will spread visibly within a day.

Freight

Twenty-six containers of water is about 63,000 lb of payload, already over legal gross once you count tractor and trailer. Twenty-six containers of caustic is 94,500 lb. Dense product loads are almost always weight-limited to fourteen or sixteen units, and finding that out at the weighbridge is expensive.

A four-line check before you buy

1. What is the specific gravity of the product? It is on the safety data sheet, section nine.
2. Multiply: gallons × 8.34 × SG, then add the tare — 127 lb for a 275, 136 lb for a 330.
3. Compare against the rack beam rating, the forklift plate at the height you will lift to, and the container's own stacking load.
4. If any of the three is close, drop to a smaller container or part-fill. Part-filling a 330 to 275 gallons is not wasteful; it is cheaper than a rack collapse.