Answer: Enter your values and the Tile Calculator returns the exact result instantly — formula, worked example, and a plain-English explanation are included below the tool.
Tiles, thinset bags & grout for floors and walls
Tile projects fail on quantity math more than on installation skill. Order too little and the lot number you need to finish may no longer be at the supplier; order too much and you are storing boxes for years. This calculator converts room dimensions — or an area you measure directly — into square footage of tile needed, then adds a waste factor you control, and finally converts coverage into boxes using the square footage printed on the carton.
The inputs match how tile is actually sold. Tile coverage is listed per box in square feet, not per piece, so the calculator's box math starts from that carton figure. The waste percentage covers cuts, breakage, and pattern matching: 10% is the standard allowance for straight lay patterns on a simple rectangular room, 15% suits diagonal (45°) layouts because edge cuts multiply, and 20% or more is prudent for large-format tile, herringbone, or rooms with heavy obstructions.
For multi-room or L-shaped areas, break the floor into rectangles, compute each, and either enter each separately or sum the areas and use the area input. The tool is indifferent to how the total was assembled — the arithmetic downstream is identical.
Area of a rectangle is length × width. A 12 ft × 10 ft room is 120 sq ft. Add waste: 120 × 1.10 = 132 sq ft for a 10% allowance. Boxes: total needed ÷ coverage per box, rounded up — at 10.5 sq ft per carton, 132 ÷ 10.5 = 12.57, so 13 boxes. Rounding up is not optional arithmetic; partial boxes are how you buy tile.
A common refinement is subtracting large fixed obstructions — a kitchen island or a tub — since tiling under a permanently cabineted island is wasted material. Do not subtract for fixtures that might move later, and never subtract so aggressively that a future repair is impossible. Keeping one full box from every install, labeled with the lot number, is cheap insurance against discontinued lines.
Different tile formats waste differently. The table below gives the customary allowances and why they exist. Note that large-format tile (anything with a side over about 15 inches) also raises installation requirements — flatter substrates and wider notched trowels — even though its per-box coverage looks efficient on paper.
Grout, thinset, and spacers scale with area too, and the calculator's per-square-foot extras handle those: typical planning figures are about one 25-lb bag of thinset per 90–100 sq ft of standard tile, and more per square foot — roughly one bag per 60–70 sq ft — for large-format tile because wider notched trowels lay more mortar, and grout quantity depends on joint width and tile thickness using the manufacturer's coverage charts.
| Tile / layout | Waste allowance | Why |
|---|---|---|
| Standard tile, straight lay | 10% | Edge cuts, minor breakage |
| Diagonal / 45° lay | 15% | Every edge tile is a diagonal cut |
| Herringbone / patterns | 15–20% | Many angled cuts, matching |
| Large-format (15 in+) | 15–20% | Cuts risk breakage; fewer spares per box |
| Natural stone | 15%+ | Vein matching, calibration variance |
Before finalizing a quantity, sketch the layout. Establish your starting line — usually centered so cut tiles at opposite walls are equal — and check where cuts land around the room's focal points. A dry layout on graph paper or a chalk line on the substrate reveals whether your pattern choice forces a sliver cut anywhere; slivers under about half a tile width look bad and often crack, and shifting the layout a few inches avoids them. This ten minutes of planning is what makes the 10% waste factor sufficient instead of optimistic.
How much extra tile should I buy?
10% over the measured area for straight-lay standard tile; 15% for diagonal or patterned layouts; 15–20% for large-format or natural stone. The extra covers cuts, breakage, and future repairs.
How do I calculate how many boxes of tile I need?
Multiply area by (1 + waste %), divide by the square footage printed on the carton, and round up. 120 sq ft at 10% waste with 10.5 sq ft boxes: 132 ÷ 10.5 = 12.57 → 13 boxes.
Should I subtract for cabinets or an island?
Subtract permanent full-height obstructions like a kitchen island or vanity, since tile under them is never seen. Keep the subtraction conservative and retain at least one spare box for future repairs.
Why keep an extra box after installation?
Tile is dye-lotted. If a tile cracks years later, an exact match may be impossible if the line or lot is discontinued — one stored box makes a seamless repair possible.
Does this work for walls and showers?
Yes — measure wall area the same way (width × height per wall, minus large openings), apply the same waste logic, and add more allowance for niche corners and trim pieces, which are sold by the linear piece, not by area.