Why the last box decides the job
Working out floor area is the easy half: length times width, plus whatever else is going down in the same product. The hard half is that flooring is sold in a unit you cannot split. Divide the area by the coverage on the carton and you get something like 15.4 boxes, and 15.4 boxes is not a thing you can buy. Round up, always, and then look at what the sixteenth box is actually doing.
That leftover is the whole point. If the last box is nearly full you are carrying repair stock, which is genuinely useful. A run sells out, and the next batch of the same product is a slightly different shade. If the last box is nearly empty you have no cushion at all, and the first plank you cut short sends you back for a box that will not match what is already down.
Two inputs decide it. The coverage per box comes off the carton in front of you, never from a website, because it moves with the board length and the pack count. The waste allowance is your own history: a plain rectangle with one doorway wants far less than a room laid on the diagonal, or a hallway full of returns and thresholds. The common mistake is measuring the room and forgetting the closet, the landing or the second doorway. The extra-area field is there so a job with two spaces takes one pass instead of two guesses.
None of this settles until you check the order against what really went down. Zeus keeps the boxes bought for a floor recorded against that job, so the next quote for the same product starts from what the last one actually took.
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