Tile is the one interior material where the waste allowance is not a rounding courtesy. Every perimeter tile is a cut, breakage is routine, and the layout you choose can turn most of the room into offcuts. This tile calculator starts at 15% for that reason.
How much to allow, and why
The allowance is doing three separate jobs, and the right figure depends on which of them dominate:
- 10% for a straight lay in a simple rectangular room with square corners.
- 15% as the working default, and what most installers order for a normal room.
- 20% or more for a diagonal or herringbone layout, where nearly every perimeter tile is cut twice, or for a room with alcoves, angles and thresholds.
Large format tile pushes it higher again, because a cut wastes more of a big tile than a small one and a broken one costs more to replace.
Whole boxes make the allowance a coarse control
This is worth understanding before you fine-tune the percentage. Tile is sold in whole boxes, so the allowance only changes your order when it pushes you across a box boundary.
On a 10 by 8 foot room at 15 square feet a box, 0% and 10% both come out at 6 boxes. At 15%, 20% and even 30% you buy 7. The percentage is a dial with only a few positions on a room this size, so set it honestly and let the box count fall where it falls.
The spare box is the point, not the overspend. That seventh box leaves about 25 square feet in hand. Tile is made in production runs with real shade variation between them, and a box from next year will not match. The tile you keep is what repairs a cracked floor without relaying the room.
Buy the whole job from one lot
Check the lot or batch number on every box before leaving the store, and confirm they match. Shade variation between production runs is normal and expected by the manufacturer, which is why the boxes carry the number at all. The Ceramic Tile Education Foundation explains the V0 to V4 shade variation ratings printed on the box, and anything at V3 or V4 varies enough that a second lot will not blend.
Mixing boxes as you lay is the usual professional habit, working out of three or four at once so that any variation within the lot is distributed across the floor rather than concentrated in one corner.
What this page does not order
Thinset, grout, backer board and edge trim are separate quantities that scale off the same area but at their own rates, and they depend on tile size, trowel notch and joint width in ways a square footage alone cannot settle.
For a floor going down in planks or boxes of laminate rather than tile, the flooring calculator handles that, and the drywall calculator covers the walls and any backer board behind a tiled surface.
Tile calculator FAQ
Fifteen percent for a normal room, 10% for a simple straight lay with square corners, and 20% or more for a diagonal or herringbone layout where nearly every perimeter tile is cut twice.
Seven boxes at 15 square feet per box with a 15% allowance, covering the 80 square foot floor and leaving about 25 square feet spare. At a 10% allowance it drops to six boxes, since tile is sold whole.
Because tile is sold in whole boxes. On a small room the allowance only changes the order when it crosses a box boundary, so 0% and 10% can give the same six boxes while 15% gives seven.
Yes. Shade varies between production runs, so check the lot number on every box and confirm they match. Working out of several boxes at once while laying also spreads any within-lot variation across the floor.