Flooring & tile calculator
How many boxes
do you actually need?
Square footage is the easy half. The number you carry to the counter is boxes — and that depends on the coverage printed on your carton, the waste your layout eats, and the floor you are not covering.
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Working out a flooring order
Three numbers decide it, and only one of them is the room.
Coverage per box
Printed on the carton, and it varies more than people expect — anywhere from about 15 to 30 ft² depending on plank size and thickness. Two boxes of the same nominal product from different lines will not match. Use the number on the box in front of you, not a remembered one.
Waste factor
10% is standard for a straight lay in a simple rectangular room. 15% for a diagonal or herringbone layout, because every run ends in a cut. More again for a room full of closets, jogs and doorways, where the offcuts get too short to use.
What you are not covering
Kitchen islands, base cabinet runs, a hearth, a built-in tub. Add them to the ledger as removing rows. Most calculators cannot subtract, which is why people end up with boxes they never open.
Rounding
Always up, always to a whole box. A 320 ft² room at 10% waste is 352 ft²; at 22.5 ft² a box that is 15.6 boxes, so you buy 16.
Buy the spare box in the same trip
This is the one that costs people money a year later. Flooring is manufactured in production runs, and colour shifts slightly between them. The box you buy today and the box you buy in eighteen months to patch a water-damaged plank will not be from the same run, and the difference is visible under daylight.
Order the waste allowance with the job, keep the offcuts, and store a full spare box flat and dry. It is the cheapest insurance in the trade.
If a supplier tells you a product is a continuous run rather than batched, ask them to put that in writing on the invoice before you rely on it.
Tile is the same maths with sharper edges
The arithmetic is identical — coverage per box, waste, round up. What changes is that tile breaks, and it breaks on the cut. A wet saw turns a marginal cut into a good one, but it still turns some tiles into scrap.
Grout and thinset are sold by coverage too, and their coverage depends on trowel notch size and joint width rather than on floor area alone, so the box count here will not tell you how many bags of thinset to buy. Ask the tile counter with your trowel size in hand.
For a room with an in-floor drain or a curbed shower base, measure the flat field area here and treat the sloped section separately — a shower pan is not a flat plane and estimating it as one comes up short.
Common questions
How many boxes of flooring do I need?
Multiply your square footage by one plus the waste factor, divide by the coverage printed on the box, then round up to a whole box. A 320 ft² room at 10% waste is 352 ft²; at 22.5 ft² per box that is 15.6 boxes, so you buy 16.
How much waste should I add for flooring?
10% for a straight lay in a simple room, 15% for diagonal or herringbone, and more for rooms with lots of closets, jogs and doorways where offcuts become unusable. The waste factor is a convention, not a rule — a complicated room can justify 20%.
Should I subtract kitchen islands and cabinets?
Yes, if the flooring will not run underneath them. Add each one as a removing row. Note that some installers run flooring under toe-kicks and appliances deliberately so a future appliance swap does not expose bare subfloor — ask yours before subtracting.
Do I measure the room or the floor?
The floor you are covering, measured at floor level inside the finished walls. Measure at the baseboard, not at eye level, and keep the tape flat so it does not read long.
The rest of the toolbox
One measurement, then whichever material you are buying. Every tool reads the same ledger.