The tool
Stack Check: how high can these gaylords stand?
Tell it the walls, the grade, what a full box weighs and where the boxes sit. It draws the stack and gives a conservative height, with the factor that limits it.
What you have
What it comes out as
How the number is worked out
| Factor | Keeps |
|---|---|
| Grade B | 75% |
| Heated warehouse | 100% |
| Up to 30 days | 85% |
| Overhangs the pallet | 100% |
| Allowed on the bottom box | 638 lb |
| Each box above weighs | 530 lb (load plus 30 lb for the box) |
Every result is a conservative estimate, not a load rating. It starts from commonly cited capacities by wall count and cuts them for published humidity and time-under-load derating, a margin for used grades and an extra cut for overhang. The reasoning is on the stacking guide.
What the answer means
Stack Check returns one of three things: a number of boxes high that is safe by our planning figures, a warning that the stack needs a closer look, or a plain “do not stack”. The figures come from published research on how box strength falls with humidity and time, and from our own conservative shares for each grade. They are not load ratings and they do not replace the box maker’s rating or your own safety rules.
If the answer is lower than you hoped, change one input at a time. The usual levers are a higher wall count, a better grade, a shorter time under load or a drier place. The tool shows what each change does, and when you are ready it hands the result to the request below. Try the same load in a heated warehouse, on an unheated dock and in a trailer, and you will see why the place matters as much as the box. A cooler is the harshest of the four, because cold air carries moisture into board that cannot get rid of it.
Two limits are worth knowing. The tool stops at three high, because a taller stack is a racking question and not a box question, and the numbers beyond three high are not ones we would stand behind. And it assumes a flat floor and a stack built square; a pallet that leans or a floor that slopes takes margin away that no table can restore. Treat the output as a first answer for a conversation with the person who runs your dock, who knows things the form cannot ask.
A worked example in words
Take a triple-wall box in Grade B, carrying 450 pounds, stacked for a month. In a heated warehouse the tool lets it go two high: the bottom box is allowed more than the one above it weighs, with margin to spare. Move the same stack to an unheated dock and the humidity and cold cut what the bottom box keeps, so the tool says one high, or no stack at all if the month becomes a quarter. The box did not change. The place did, and the place decides.
Try the same arithmetic with a 5-wall box and the answer moves the other way: the higher wall count starts from a bigger rating, so it keeps more after the same cuts. Wall count raises the ceiling; grade, place and time lower it; and the stack height is whatever is left after the bottom box has carried the boxes above it. If you know the box maker’s rated capacity, enter it, and it replaces the wall-count figure. If you have an overhang, because the box is wider than its pallet, tick it, and the tool cuts the strength to eighty percent of what it was.
Reading the warnings
When the tool shows a warning, it is saying one of three things. A condensation warning means the place is cold and damp enough that the board will take on water, so the answer is a drier bay or a shorter stand. A step-up warning means the load is more than the box can reasonably carry at the rating it started from, so the answer is a higher wall count. An overhang warning means the box is wider than its pallet, so the answer is a different footprint or a smaller number of boxes high.
Each of these has its own cure and each one shows up on real docks every winter. If you think a result is too cautious for your conditions, send a request with the numbers and what you see on your floor, and the desk will look at it with you.
Who the tool is for
Stack Check is written for a person who has boxes and a floor and wants to know how many to put on top of each other. It suits a receiving clerk, a plant supervisor, a farm manager or an owner-operator. It does not suit anyone designing a racking system, rating a package for transport or certifying a dangerous-goods container. For those jobs the maker’s documents and a qualified engineer come first, and the numbers here are only a sanity check beside them.
The wall counts offered are two, three, four and five, because those are the builds the trade lists. The places are a heated warehouse, an unheated dock, a cooler, a freezer, a trailer and covered outdoor storage. The times run from a day or two to a long stand. Each choice changes the factor the tool applies, and the table above shows the factors one by one so you can see which of them is limiting your stack.
Sources behind the factors
The humidity and time-under-load factors come from published testing on corrugated board: strength falls by about half at 90 percent relative humidity, and by nearly 45 percent after 90 days under load in humid conditions. The overhang factor follows research from Virginia Tech showing that effective box compression strength decreases as pallet overhang increases. The starting capacities by wall count are the ranges commonly cited by box sellers. The grade shares and the cut for a condensation-prone place are this site’s own cautious assumptions, and they are the part most worth challenging if your own experience says otherwise.