How much extra tile should I buy for waste?

Roughly 10% for a straight / grid layout, 15% for a diagonal layout, 20% for a herringbone / complex layout — cuts, breakage, and the offcuts trimmed at every wall all come out of that allowance. On a 120 ft² room in 12 × 12 in tile, that waste adds 12 tiles over the bare 120-tile minimum.

How many 12x12 tiles in 100 square feet?

One hundred, exactly, because a 12 × 12 in tile covers exactly one square foot. Add the usual 10% waste allowance and that becomes 110 tiles, or 11 boxes at 10 tiles per box.

How many tiles are in a box?

It varies by manufacturer and tile size — 10 tiles per box is a common figure for 12 × 12 in tile, but a large-format 24 × 24 in tile often ships two to four per box, and a mosaic sheet counts by the sheet instead. Always check the box label; this calculator assumes 10 unless you change it, and box counts always round up because a supplier will not split one open.

How do I calculate tile for a backsplash?

The same way as a floor: multiply the backsplash's length by its height to get the area, then divide by the tile's area and add waste. A 15 ft² backsplash in 4 × 4 in tile needs 135 tiles before waste, 149 with 10% added — 15 boxes at 10 tiles per box. Measure around outlets and windows as if they were not there; only subtract an opening if it is large.

How much does it cost to tile a floor?

Multiply the order area — room area plus the waste allowance — by the price per square foot. At a typical $3.00 per square foot for the tile alone, a 120 ft² floor with 10% waste costs about $396. That figure is materials only: grout, thin-set mortar, spacers, and labor if you hire it out are separate line items.

How many 12x24 tiles do I need?

A 150 ft² room in 12 × 24 in tile (2 ft² each) needs 83 tiles with a straight layout's 10% waste, or 87 tiles if the same room is laid on the diagonal at 15% waste — 9 versus 9 boxes at 10 tiles per box.

Do I need more tile for a diagonal layout?

Yes — a diagonal layout leaves a triangular offcut at every wall that a straight layout does not, so it typically carries 15% waste against 10% for a straight run. On a 150 ft² room in 12 × 24 in tile that is the difference between 83 tiles and 87 tiles for the exact same floor.

Construction

Tile Calculator

Tile count is room area divided by one tile's area, plus a waste allowance for cuts and breakage. Enter a room's dimensions or its area, pick a tile size and layout, and get the tiles, boxes and cost — or flip the tool around and work out how much room the boxes you already own will cover.

Room size

Length

Width

How many identical rooms?

Tile size

1.00 ft² per tile

Layout & waste

Waste allowance

Ordering

Tiles per boxPrice per ft²

Price per boxOptional — shown as a second cost path if the tile is priced by the box

Tiles needed

132

12 × 12 in · Straight / grid layout

Room area

120.0

Before waste

120 tiles

Boxes to buy

14 boxes

10% waste included

120 → 132 tiles, 10 per box

Estimated material cost

By area

$396

120.0 ft² @ $3.00

By box

—

14 boxes @ —

Try a room

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Tile area = (width × height) ÷ 144. Box counts always round up — you cannot buy part of a box.

The basics

How tile quantity is worked out

Every tile estimate is the same two divisions: find how many bare tiles fill the floor, then find how many boxes hold that many tiles. What changes from job to job is the waste percentage, which depends entirely on the layout.

tiles = area ÷ tile area

Tile count comes from two areas

Divide the room’s area by one tile’s own area — width times height, both converted to the same unit first. That bare count is the theoretical minimum with zero cuts and zero breakage, which no real job ever achieves.

120 ft² ÷ 1.00 ft² = 120 tiles

boxes = tiles ÷ per box, rounded up

Boxes always round up

Add the waste allowance to the tile count first, then divide by how many tiles come in one box. A supplier will not open a box to sell part of it, so this division always rounds up, never to the nearest whole number.

132 ÷ 10 = 13 → 14 boxes

Method

How to size a tile order by hand

Four steps take you from a tape measure to a number you can read off to a tile shop.

1
Find the room's area in square feet
Multiply length by width once both are in feet, or read the area straight off a floor plan. Add up more than one room if they are being tiled the same way.
10 ft × 12 ft = 120 ft²
2
Find one tile's area
Multiply the tile's width and height in inches, then divide by 144 — the number of square inches in a square foot.
12 in × 12 in ÷ 144 = 1.00 ft²
3
Divide, add waste for the layout, round up
Divide room area by tile area for the bare count, then add ten to twenty per cent depending on the layout before rounding up to a whole tile.
120 × 1.10 ÷ 1.00 = 132 tiles
4
Divide by tiles per box
Divide the tile count by how many tiles ship in one box and round up. Multiply the order area by the price per square foot for a materials cost.
132 ÷ 10 = 14 boxes

Worked examples

The same 120 ft² room, three tile sizes

Identical room, identical 10% waste allowance — only the tile size changes. Larger tiles mean fewer pieces but the same square footage of material.

12 × 12 in12 × 24 in6 × 24 in plank

Where it shows up

Every job this math covers

The same division works whether the surface is a floor, a wall, or a run of counter — only the tile size and the waste allowance change.

Bathroom floors and shower walls

Small rooms with lots of corners, curbs, and niches drive the waste allowance up even on a straight layout, because every cut edge disappears into an offcut pile.

Kitchen backsplash

A backsplash is a wall run measured in square feet like any other surface, just smaller — and it is where mosaic sheets and 4 × 4 in tile do most of their work.

Whole-home flooring

Large-format tile in continuous rooms keeps the tile count low and the grout-line count lower, which is why 12 × 24 and 24 × 24 in sizes dominate open-plan floors.

Reference

Common tile sizes and waste by layout

The tile counts every search for “how many tiles in 100 square feet” is really asking for, across the sizes people actually buy, plus the waste convention each layout carries.

Tile size	Area per tile	Tiles per 100 ft²	Typically used for
12 × 12 in	1.00 ft²	100	The all-purpose floor tile
12 × 24 in	2.00 ft²	50	Large-format floors, fewer grout lines
6 × 24 in	1.00 ft²	100	Wood-look plank flooring
18 × 18 in	2.25 ft²	45	Larger rooms, entryways
24 × 24 in	4.00 ft²	25	Large-format floors and patios
4 × 4 in	0.11 ft²	900	Backsplash and shower walls
3 × 6 in	0.13 ft²	800	Subway tile, kitchen and bath walls

No waste added — this is the bare tile count for 100 ft² of surface.

Layout	Default waste	Why
Straight / grid	10%	Tiles run square to the walls — the simplest layout and the least cutting.
Diagonal	15%	Tiles set at 45° to the walls, which leaves a triangular offcut at every edge.
Herringbone / complex	20%	Herringbone, basket-weave, or a pattern mixing sizes — the most cuts of any layout.

Grout & spacing

Grout is a separate order, sized by joint width

Tile count and grout quantity are two different calculations — grout scales with the total joint length and width, not with how many tiles you bought. The joint width itself is mostly a convention of the tile type.

Tile type	Typical joint	Why
Polished / rectified porcelain	1/16 in (1.5 mm)	Edges are cut dead square, so almost no gap is needed
Standard ceramic or porcelain floor	1/8 in (3 mm)	The residential default for 12×12 and 18×18 tile
Natural stone (travertine, slate)	3/16 in (5 mm)	Stone edges vary more than manufactured tile
Handmade or subway wall tile	1/16–1/8 in (1.5–3 mm)	Tighter joints read as more traditional
Large-format plank (6×24, 12×24)	3/16–1/4 in (5–6 mm)	A wider joint hides the lippage long tiles are prone to
Exterior / pool deck	1/4–3/8 in (6–10 mm)	Wider joints allow for more thermal movement

Spacers set the joint width during installation and are sold by that same width — buy them with the tile, not as an afterthought once the thin-set is already down.

Worth knowing

Rules worth remembering

Six facts that turn a tile order from a guess into a decision, none of them printed on the box.

area ÷ 144

Tile area always starts in inches

A tile’s dimensions are sold in inches, but area lives in square feet. Skipping the divide by 144 inflates the tile count by more than a hundredfold, which is an unmistakable sign the units were never converted.

fewer, bigger tiles

Larger format means fewer boxes, not less material

A bigger tile covers the same floor with a lower tile count, but the square footage of material — and its cost — barely moves. Fewer boxes mostly means fewer grout lines, not a cheaper job.

120 ft²: 132 tiles of 12 × 12 in vs 66 of 12 × 24 in

always round up

Tiles and boxes are ceilings, never averages

A tile count of 131.4 buys 132 tiles, and 132 tiles at ten per box buys fourteen boxes, not thirteen and a bit. Rounding down anywhere in the chain is how a job stalls one tile short.

waste follows the layout

The layout sets the waste, not a flat rule

Straight, diagonal and herringbone leave different amounts of unusable offcut at the walls. Picking the waste percentage before picking the layout gets the causality backwards.

one dye lot

Buy the whole job from one production run

Ceramic and porcelain tile is fired in batches called dye lots, and color drifts slightly between them. A box bought later to finish a short order rarely matches exactly.

keep a spare box

Future repairs need tile from today, not next year

Dye lots and even whole product lines get discontinued. Storing one unopened box is far cheaper insurance than re-tiling a room because a single cracked tile can no longer be matched.

Quick chart

Tiles and boxes for common room sizes

The answer to “how many tiles for a 10 × 12 room” and every common size around it, using 12 × 12 in tile with a straight layout’s 10% waste allowance and 10 tiles per box. Larger or smaller tile shifts the tile count but not the underlying area — use the calculator above for any other size.

Room	Area	Tiles (10% waste)	Boxes
5 × 7 ft bathroom	35.00 ft²	39	4
8 × 10 ft bedroom	80.00 ft²	88	9
10 × 10 ft room	100.0 ft²	110	11
10 × 12 ft room	120.0 ft²	132	14
12 × 12 ft room	144.0 ft²	159	16
12 × 15 ft room	180.0 ft²	198	20
15 × 20 ft room	300.0 ft²	330	33
20 × 20 ft room	400.0 ft²	440	44

A 100 ft² wall in 3 × 6 in subway tile needs 880 pieces at the same 10% waste — small tile always multiplies the count fastest.

Common mistakes

Where tile orders go wrong

Six errors account for almost every mid-job supply run and every visible seam between batches.

order 10%+ over

Buying the exact tile count

Cuts, breakage, and the box you drop on day one all eat into the count. Ordering to the exact number is how a job stalls two tiles short with the pattern half-cut.

measure the floor, not the box

Trusting the box coverage label

A box printed as covering fifteen square feet is a nominal figure for the tile alone — it says nothing about your waste percentage. Divide the room area by the tile's own footprint instead.

same dye lot

Buying tile across two trips

Ceramic and porcelain tile is fired in batches, or dye lots, and shade drifts between them. Buying the whole job at once, from the same lot number, avoids a visible seam where the batches meet.

keep a full box

Using every tile you bought

Future repairs need tile from the same run, and dye lots stop being sold within a year or two. Keeping one unopened box in storage is cheaper than re-tiling a whole floor after one cracked piece.

diagonal costs more

Pricing a diagonal layout like a straight one

A 45° layout leaves a triangular offcut at every wall, which is why it carries a higher waste allowance. Skipping that adjustment is a common source of a mid-job supply run.

grout is separate

Forgetting to budget for grout and spacers

Tile count only covers the tile itself. Grout, spacers, thin-set mortar, and a sealant for natural stone are separate line items that scale with area, not with tile count.

FAQ

Common questions

Divide the room's area in square feet by one tile's area in square feet, then add a waste allowance for cuts and breakage before rounding up to a whole tile. A 120 ft² room laid with 12 × 12 in tile needs 120 tiles before waste, or 132 with the usual 10% waste allowance — 14 boxes at 10 tiles per box.

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