Construction · By ListCalc Editorial Team · Jun 16, 2026 · 6 min read

How Much Tile Do I Need?

Every tile estimate is an area calculation plus a judgement call about waste. The second part is where people get it wrong, and it is the reason for the second trip to the store.

The area is the easy part

Measuring a rectangular room takes ten seconds. The number that decides whether you make a second trip to the store is the waste factor — the extra tile you buy knowing some of it will end up as offcuts, breakage and spares.

Area = length × width
Order = area × (1 + waste %)
Boxes = order ÷ coverage per box, rounded up

For an L-shaped room, split it into rectangles, work out each one and add them together. Subtract nothing for a kitchen island or a bath unless it is genuinely permanent and larger than about 10 square feet — small deductions get eaten by waste anyway.

Waste factors that actually apply

Waste is not a single number. It depends far more on the layout pattern and the shape of the room than on the tile itself.

Situation	Add	Why
Straight lay, square room	10%	Perimeter cuts only
Straight lay, irregular room	15%	More edges, more part-tiles
Diagonal (45°) lay	15%	Every perimeter tile is cut twice
Herringbone or chevron	20%	Heavy cutting at all four edges
Large format (24 in and up)	15%	An offcut is rarely reusable
Mosaic sheets	10%	Sheets can be trimmed tile by tile
Patterned or directional tile	+5%	Alignment forces discards

These stack. A herringbone floor in an irregular room is a 20–25% job, not a 10% one.

From room size to boxes

Coverage per box varies — 15 to 16 square feet is typical for a 12 in floor tile, but always read the box. The last column assumes 15.5 sq ft per box at a 10% waste factor.

Room	Area	+10%	+15%	+20%	Boxes (10%)
8 × 10 ft	80 sq ft	88	92	96	6
10 × 12 ft	120 sq ft	132	138	144	9
12 × 12 ft	144 sq ft	158	166	173	11
12 × 15 ft	180 sq ft	198	207	216	13
14 × 16 ft	224 sq ft	246	258	269	16
16 × 20 ft	320 sq ft	352	368	384	23
20 × 24 ft	480 sq ft	528	552	576	35

Always round up to whole boxes and buy the surplus in the same purchase. Tile is made in batches, and a box bought six months later can be visibly off-shade even with an identical product code.

The materials nobody budgets for

Thin-set mortar. Roughly one 50 lb bag per 40–60 sq ft with a 1/4 in trowel; large-format tile with a bigger trowel can halve that coverage.
Grout. Driven by joint width, tile size and tile thickness — narrow joints on big tiles use very little, wide joints on small tiles use a lot.
Backer board. Sold in 3 × 5 ft sheets (15 sq ft), so a 144 sq ft floor needs 10 sheets before waste.
Trim and transitions. Bullnose, edge profiles and thresholds are priced per linear foot, so measure perimeter separately from area.

Run your own dimensions through the tile calculator, or use the flooring calculator if you are comparing tile against plank or sheet goods sold by the carton.

Where estimates go wrong

Measuring the room, not the tiled area. Tiling up a shower wall or a backsplash is a separate area calculation.
Nominal versus actual size. A 12 inch tile is often 11 7/8 in, with the grout joint making up the difference. Use the box coverage figure, never tile count × nominal size.
Forgetting spares. Keep at least half a box after the job. A cracked tile in year three is unfixable without a match.
Ignoring the layout. Where you start the first row changes how much gets cut. Centring the pattern looks better and usually wastes more.

The same measure-then-add-waste logic applies to almost every surface material — see how much paint a room needs for the coverage-rate version of the same problem.

Run your own numbers

Tile Flooring

FAQ

How much extra tile should I buy?

Ten percent over the measured area for a straight lay in a square room, 15% for a diagonal lay or an irregular room, and 20% for herringbone or chevron. Add another 5% for patterned tile that has to be aligned.

Do I subtract cabinets and fixtures from the area?

Only for permanent features larger than roughly 10 square feet, such as a kitchen island or a built-in tub. Smaller deductions are absorbed by the waste factor, and subtracting them tends to leave you short.

How many tiles are in a box?

It varies by size and manufacturer, so use the square-foot coverage printed on the box rather than counting tiles. A 12-inch floor tile box usually covers about 15 to 16 square feet.

Should I buy all the tile at once?

Yes. Tile is produced in batches and shade varies between them, so a replacement box bought later may not match. Buy the full quantity including waste in one purchase and keep the leftovers.

How much thin-set and grout will I need?

As a rough guide, one 50 lb bag of thin-set covers 40 to 60 square feet with a 1/4 inch notched trowel, and less with the larger trowel that big-format tile requires. Grout depends on joint width, tile size and tile thickness, so check the coverage table on the bag.

Sources

Primary references used for the figures and rules on this page.

Tile installation standards and the TCNA Handbook — Tile Council of North America