How Much Flooring for an 18x18 Room?
Boxes to order
16 boxes
324 square feet of floor, ten percent waste, boxes of 22.5 square feet.
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How that number is worked out
These are the figures this page was built with and every line the calculator produces from them. Change anything above and all of it moves.
- Floor area324 sq ft
- Coverage per box or carton22.5 sq ft
- Waste allowance10 %
Boxes to order16 boxes
| Floor area | 324 sq ft |
|---|---|
| With 10% waste | 356.4 sq ft |
| Boxes at 22.5 sq ft | 16 |
| Coverage bought | 360 sq ft |
| Left over | 36 sq ftkeep it for repairs |
The material list this produces
| Flooring, boxes | 16 |
|---|---|
| Underlayment, sq ft | 324 |
| Transition strips, each | 2 |
Waste allowance compared
Waste is set by how you lay it, not by how careful you are. Straight lay to herringbone, same room.
| Waste allowance | Boxes to order | With 10% waste | Left over |
|---|---|---|---|
| 5% | 16 boxes | 340.2 sq ft | 36 sq ft |
| 10% | 16 boxes | 356.4 sq ft | 36 sq ft |
| 15% | 17 boxes | 372.6 sq ft | 58.5 sq ft |
| 20% | 18 boxes | 388.8 sq ft | 81 sq ft |
What else matters here
Three hundred and twenty four square feet with ten percent is 356.4, sixteen cartons, 360 bought. Only 36 square feet spare on a square room, so if this is going in as tile, allow more.
Tile is laid from the middle outward rather than from a wall, because a square room shows a bad layout in both directions at once. Snap two chalk lines through the center of the room at right angles, dry lay a row each way without adhesive, and see where the cuts land at all four walls.
If the last tile at a wall is a narrow sliver, shift the center line by half a tile and the cuts move to a usable width on both sides. Do it for both axes. The grout line is part of the layout too: a 1/8 inch joint across eighteen feet of twelve inch tile adds close to two inches, which is enough to turn a clean edge into a sliver if it was not counted.
What this calculator assumes
- 10 percent waste covers a straight lay in a simple rectangle. Go to 15 for a diagonal or herringbone lay, and 20 if the room is cut up with closets and angles.
- Buy the whole job in one delivery. Dye lot and batch shade move between production runs, and a single replacement box six months later will not match.
Questions people ask
How many boxes of flooring for an 18x18 room?
About 16 boxes at 22.5 square feet each, covering 324 square feet with ten percent waste.
Where do you start laying tile in a square room?
From the center. Snap two chalk lines at right angles through the middle, dry lay both ways, and check what the cuts look like at all four walls before mixing any thinset.
Do grout lines change the tile count?
Yes. An eighth inch joint across eighteen feet of twelve inch tile adds nearly two inches, which is enough to move a border cut from comfortable to a sliver.
The flooring calculator takes any dimensions you like and hands back the same list.