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How Many 18×18 Inch Tiles for a 20×20 ft Area?

A 20 by 20 foot area needs this many 18 by 18 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: 196 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	440 tiles	1,760 tiles	220 tiles	196 tiles
Tile size	12″ × 12″	6″ × 6″	12″ × 24″	18″ × 18″

What a 20×20 ft area in 18″ × 18″ tiles actually involves

At 400 ft² this is a whole-floor job. 196 tiles is roughly 1,760 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 400 ft², or 440 ft² with your 10 percent waste allowance. Each 18″ × 18″ tile covers 2.25 ft², so you need 196 tiles — about 30 boxes at the 15 ft² per box on the label.

At 18″ × 18″ you are into large-format work, and the rules change. 14 tiles across and 14 down means very few joints (533 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: 14 tiles across, 14 down

Layout	Value	Note
Tiles across the 20 ft side	14	13 full tiles plus a 6 in cut
Tiles down the 20 ft side	14	13 full tiles plus a 6 in cut
Full grid	196 tiles	before waste, if every tile were whole
Edge tiles to cut	about 27	the perimeter run, where the cuts live
Total to buy	196 tiles	440 ft² ÷ 2.25 ft² per tile

The room is square at 20 × 20 ft, so the grid is symmetrical and a centred layout will look almost the same from any corner. A square tile in a straight lay gives you one clean grid with no pattern to line up, which is the fastest way to lay this floor.

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	533 ft	1.3 ft of joint per ft² with 18″ × 18″ tiles
Sanded grout	about 6 × 25 lb bags	roughly 134 lb at a 1/8 in joint, 1/4 in deep
Thinset mortar	5 × 50 lb bags	about 95 ft² per 50 lb bag at a 1/4 in notch
Tile weight	about 1,760 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: an 18″ × 18″ tile puts 1.3 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

196 tiles is 30 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 533 ft of joint to look after.

Common questions

How many 18×18 inch tiles do I need for a 20×20 ft area?

196 tiles. The floor is 400 ft² and each 18″ × 18″ tile covers 2.25 ft², so 440 ft² with your 10 percent waste allowance divides out at 196 tiles — about 30 boxes at 15 ft² per box.

How many boxes of tile is that?

30 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 20×20 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 14 tiles across and 14 down, so roughly 27 tiles are on an edge and will be cut.

How much grout and thinset do I need?

About 6 × 25 lb bags of grout and 5 × 50 lb bags of thinset, based on 533 ft of grout joint and a 1/4 in notch trowel. 18″ × 18″ tile puts 1.3 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 18×18 inch tiles in a 20×20 ft room?

Centre the grid and work outwards. You need 14 tiles across and 14 down; the edge cuts are the last 6 in of the 20 ft side and the last 6 in of the 20 ft side. If those cuts come out as slivers, shift the centre line by half a tile to balance them.