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How Many 12×24 Inch Tiles for a 15×15 ft Area?

A 15 by 15 foot area needs this many 12 by 24 inch tiles and boxes, including waste, grout and thinset. Here is the answer, plus a calculator you can adjust if your measurements are slightly different.

Answer: 124 tiles

How it changes with tile size

Same area, different tile size:

Tile size	12×12 in	6×6 in	12×24 in	18×18 in
Tile needed	248 tiles	990 tiles	124 tiles	110 tiles
Tile size	12″ × 12″	6″ × 6″	12″ × 24″	18″ × 18″

What a 15×15 ft area in 12″ × 24″ tiles actually involves

At 225 ft² this is a whole-floor job. 124 tiles is roughly 990 lb of material to carry in, spread and grout — plan it over more than one day, and work in sections you can finish before you walk on them. Large areas also mean the tile has to be flat and the substrate has to be right; movement in a floor this size shows up as cracked tiles at the joints.

The floor is 225 ft², or 248 ft² with your 10 percent waste allowance. Each 12″ × 24″ tile covers 2.00 ft², so you need 124 tiles — about 17 boxes at the 15 ft² per box on the label.

At 12″ × 24″ you are into large-format work, and the rules change. 15 tiles across and 8 down means very few joints (338 linear ft in total) and a very flat looking floor — which is exactly why the substrate has to be flat, not merely sound. Large format tiles do not follow a dip; they rock on it. Use a 3/8 in notch trowel, back-butter every tile, and use a levelling clip system. Expect to lose more to cuts as well: at this size a mistake is an expensive mistake.

Your layout: 15 tiles across, 8 down

Layout	Value	Note
Tiles across the 15 ft side	15	15 full tiles with a full tile edge
Tiles down the 15 ft side	8	7 full tiles plus a 12 in cut
Full grid	120 tiles	before waste, if every tile were whole
Edge tiles to cut	about 22	the perimeter run, where the cuts live
Total to buy	124 tiles	248 ft² ÷ 2.00 ft² per tile

The room is square at 15 × 15 ft, so the grid is symmetrical and a centred layout will look almost the same from any corner. A 12″ × 24″ tile in a straight lay has an obvious direction. Decide which way it runs before you mix any adhesive, and keep that direction through doorways — the eye follows it.

Start from the centre, not from a wall. Walls are never square, and a layout built off one wall ends up with a widening wedge of cut tiles on the far side. Strike a centre line in both directions, dry-lay a row, then adjust the starting line so the cuts on opposite edges come out the same width.

Grout, thinset and weight

Item	Quantity	How it is worked out
Grout joint length	338 ft	1.5 ft of joint per ft² with 12″ × 24″ tiles
Sanded grout	about 4 × 25 lb bags	roughly 85 lb at a 1/8 in joint, 1/4 in deep
Thinset mortar	3 × 50 lb bags	about 95 ft² per 50 lb bag at a 1/4 in notch
Tile weight	about 990 lb	4 lb per ft² installed; porcelain and stone are heavier
Notch trowel	3/8 in	matched to the tile size

Grout is the figure people get wrong, and it is because of joint length rather than floor area: a 12″ × 24″ tile puts 1.5 ft of joint into every square foot. Check the coverage printed on the bag you buy — the numbers above assume a 1/8 in joint, and widening to 3/16 in adds roughly half again. Buy a spare bag: a second bag from a different batch can be a shade off, and part-used bags are the only thing harder to match than discontinued tiles.

Buying the boxes

124 tiles is 17 boxes if every box really covers 15 ft². Do not trust the tile count in a box — boxes are labelled by coverage in square feet, and the tile count changes with size and with the manufacturer's packing. Read the ft² figure from the box you are actually going to buy, and if it differs from 15, rework the count from the tile size above rather than the box.

Buy the whole floor in one purchase and check the dye lot code on every box before you leave the store. Tiles are made in batches that vary slightly in shade and calibration, they get discontinued constantly, and a floor laid from two different lots shows the seam. Keep the leftovers. A cracked tile three years from now is unfixable unless you have a spare in a matching lot, and one box of spares is the cheapest insurance in the job.

Laying it

Make the substrate right first. Tile will not fix a bouncy floor or a damp wall. Backer board or a tile membrane over the subfloor, and a waterproof membrane in any wet area, before a single tile goes down.
Find the centre of the room, strike both centre lines at right angles, and dry-lay a row in each direction. Adjust the start so the edge cuts are even.
Spread adhesive in small areas — a square metre at a time — with the flat side of the trowel first and then the notched side. Adhesive that has skinned over before the tile lands will not bond.
Back-butter every tile, and press with a slight twist to collapse the ridges. Aim for full coverage, not just contact at the corners.
Use 1/8 in to 3/16 in spacers plus a levelling clip system. Once the adhesive sets, the only way to fix a lip is to break the tile out.
Let the adhesive cure before grouting — 24 hours is normal, longer in a cold or damp room.
Grout with a rubber float held at 45 degrees, work it in small sections, and wipe the surface before it sets on the tile face. Haze comes off with a dry cloth, set grout does not.
Seal cement-based grout once it is fully cured, and seal natural stone before it is laid. This floor has about 338 ft of joint to look after.

Common questions

How many 12×24 inch tiles do I need for a 15×15 ft area?

124 tiles. The floor is 225 ft² and each 12″ × 24″ tile covers 2.00 ft², so 248 ft² with your 10 percent waste allowance divides out at 124 tiles — about 17 boxes at 15 ft² per box.

How many boxes of tile is that?

17 boxes at 15 ft² per box. Always confirm the coverage on the label of the box you are buying rather than counting tiles — packing varies by manufacturer, and it is the square footage that matters.

How much waste should I allow for a 15×15 ft floor?

Your page is worked at 10 percent. For a straight lay in a rectangular room 10 percent is normal; go to 15 percent for a diagonal or herringbone layout, for a room full of doorways and fittings, or for large-format tiles where a single miscut is expensive. This floor needs 15 tiles across and 8 down, so roughly 22 tiles are on an edge and will be cut.

How much grout and thinset do I need?

About 4 × 25 lb bags of grout and 3 × 50 lb bags of thinset, based on 338 ft of grout joint and a 1/4 in notch trowel. 12″ × 24″ tile puts 1.5 ft of joint in every square foot, so smaller tiles and wider joints both use more grout than this estimate.

How do I lay out 12×24 inch tiles in a 15×15 ft room?

Centre the grid and work outwards. You need 15 tiles across and 8 down; the edge cuts are the none on the 15 ft side and the last 12 in of the 15 ft side. If those cuts come out as slivers, shift the centre line by half a tile to balance them.