The formula

Area: length × width of the floor, or width × height of the wall.
Tiles for the area: area ÷ the space one tile takes with its joint, (tile length + joint) × (tile width + joint).
Plus waste: times 1 + the waste allowance for the pattern, rounded up to a whole tile.
Never fewer than the layout: the calculator also lays the tiles in the room, centred so the cuts at opposite walls match, and counts one tile per full or cut position. If that is more than the area count, it wins.
Boxes: tiles ÷ tiles per box, rounded up.
Grout (kg/m²): (A + B) ÷ (A × B) × C × D × 1.6, with tile length A, width B, thickness C and joint width D in millimetres, times the area.
Thinset: area ÷ the area one bag covers with your trowel, rounded up.

Assumptions and sourcesWaste: 10% for a straight layout and 15% for diagonal, from Floor & Decor ("at least 10% overage for standard layouts and 15% for diagonal, herringbone, or other pattern installations"; undated, checked 11 October 2026). 15% for brick and 20% for herringbone, from Fireclay Tile's Tile School (6 September 2015: "15% extra for field tile orders (such as subway tile)", "20% overage for projects that include patterns like herringbone"). No tile maker or standards body we found publishes a figure for brick layouts as such. Grout: the consumption formula in MAPEI's Ultracolor Plus technical data sheet; 1.6 is that grout's density. It matches MAPEI's Keracolor S sanded grout data (26 February 2026: 25 lb bags, joints 1/8 to 5/8 in); Keracolor U unsanded is for 1/16 to 1/8 in. Thinset: the low end of LATICRETE LHT PLUS's data sheet (DS-109-1024), per 50 lb bag: 80 to 95 ft² with a 1/4 × 1/4 in notch, 60 to 70 ft² with 1/4 × 3/8 in, 40 to 47 ft² with 1/2 × 1/2 in. MAPEI's trowel FAQ puts tiles with any side over 15 in on the 1/2 in notch. Box and thickness: Daltile's Portfolio sales sheet (02/24) lists its 12 × 24 in porcelain as 5/16 in thick, 9 pieces to a carton. Use the figures on your own products: every field can be changed.

Worked example

A 12 × 10 ft floor (120 ft²) in 12 × 24 in porcelain, 5/16 in thick, with 1/8 in joints, laid straight. One tile with its joint takes 24⅛ × 12⅛ in, 2.03 ft², so the area needs 59.1 tiles; with 10% waste that is 65.0, so 65 tiles, or 8 boxes of 9. Laid from the centre, the floor has 32 full tiles and 28 cut ones (12 ft is not a whole number of 24⅛ in tiles, so every row and column ends in a cut), 60 positions in all, which leaves 5 spare. Grout: (610 + 305) ÷ (610 × 305) × 7.9 × 3.2 × 1.6 = 0.20 kg/m², times 11.1 m², is 2.2 kg (4.9 lb), one 25 lb bag of sanded grout. Thinset with a 1/2 × 1/2 in trowel (the tile is longer than 15 in): 120 ÷ 40 = 3 bags.

Tiles for a 12 × 10 ft floor (120 ft²), 5/16 in tile, 1/8 in joints, worked with the calculator
Tile (in)	Pattern and waste	Full	Cut	Tiles to buy	Grout	Thinset
12 × 12	Straight, 10%	80	40	130	6.5 lb	2 bags
12 × 24	Straight, 10%	32	28	65	4.9 lb	3 bags
18 × 18	Straight, 10%	30	26	58	4.3 lb	3 bags
24 × 24	Straight, 10%	12	18	33	3.3 lb	3 bags
3 × 6 subway	Brick, 15%	832	124	1,039	19.5 lb	2 bags
6 × 24 plank	Brick, 15%	81	49	135	8.1 lb	3 bags
12 × 24	Herringbone, 20%	38	41	79	4.9 lb	3 bags
12 × 12	Diagonal, 15%	97	46	143	6.5 lb	2 bags

Thinset is 50 lb bags with a 1/4 × 3/8 in trowel for tiles up to 15 in (1/4 × 1/4 in for the subway tile) and 1/2 × 1/2 in above. In the herringbone and diagonal rows the layout itself needs more positions (79 and 143) than the area and waste give (71 and 136), so the layout count is what to buy. Large tiles in a small room are mostly cuts: a 24 × 24 in tile leaves only 12 whole tiles on this floor. In metric, a 3.6 × 3 m floor in 60 × 30 cm tiles 8 mm thick, 3 mm joints, straight, needs 66 tiles and about 2.1 kg of grout.

Before you order

Buy from one lot. Shade varies between production runs; the lot or shade number is on the box. The spare tiles are your repair stock, from the same lot.
Check the layout on the floor. Dry-lay a row each way from the centre. If a wall ends in a sliver, shift the starting line by half a tile. The calculator tries both (a tile or a joint on the centre line) and keeps the one with the bigger edge pieces.
Walls: switch the surface to Wall and enter the wall's width and height. Take a window or a tub out by tiling each area separately.
Grout type: MAPEI's sanded grout is for joints of 1/8 in and wider, its unsanded grout for 1/16 to 1/8 in. The calculator names the type from your joint; check your own grout's range.

Every room at once

FloorGen's Schedules and budget panel (in the account menu) lists the floor area of every room with a tile floor, with an editable waste percentage, so a whole house is one table. See materials estimate from a floor plan for a worked example, and the 5 × 8 bathroom layout for a small bath.

Questions

How many tiles do I need for a 10 × 12 room?

120 ft² of 12 × 24 in tile with 1/8 in joints is 59 tiles before waste. With 10% for a straight layout, buy 65 (8 boxes of 9). With 12 × 12 in tile, buy 130.

How much extra tile should I buy?

Retailers and tile makers suggest about 10% for a straight layout, 15% for diagonal or a subway (brick) layout and 15 to 20% for herringbone. Small rooms and large tiles need more, because most tiles at the walls are cut; the calculator never buys fewer tiles than its layout lays.

Do I count the grout lines?

Yes, a little. A tile with its joint covers slightly more than the tile alone, so counting the joint means fewer tiles: 12 × 24 in tile on 1/8 in joints covers 2.03 ft² each, not 2.

How much grout do I need?

It depends on the joint's width and depth and the tile size. MAPEI's formula, (A + B) ÷ (A × B) × thickness × joint × 1.6 kg/m² in millimetres, gives about 5 lb for 120 ft² of 12 × 24 in tile 5/16 in thick with 1/8 in joints, and four times that for 3 × 6 subway tile.

How many bags of thinset for 100 square feet?

With a 1/4 × 1/4 in notch trowel a 50 lb bag covers roughly 80 to 95 ft², and with 1/4 × 3/8 in 60 to 70 ft², so 2 bags either way. Large tiles on a 1/2 × 1/2 in notch take 40 to 47 ft² a bag: 3 bags. Check your mortar's bag.

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