Tile calculator for floors and walls

Measuring floors, walls and backsplashes

The calculator works with rectangles. Each row is one surface: a floor, a wall, a shower wall, a backsplash. For a floor, enter the length and width of the room. For walls, add one row per wall, using the height the tile actually goes up to. In a bathroom that is often 4 ft or 8 ft, not the ceiling. A kitchen backsplash is usually the run of counter times about 18 in.

Doors and windows go under openings, and we take them off the total. Floors rarely have anything to take off. Niches, boxed-in pipes and window returns are the opposite: add them as extra surfaces, because they are tile to set, and most of it is cut.

An L-shaped room is two rectangles. If you are painting the walls above the tile as well, the paint calculator takes the same measurements.

How many tiles do I need? How the calculator works

Tiles are counted with the grout joint included. A 12 × 24 in tile with a 1/8 in joint takes up 12.125 × 24.125 in, which is 2.03 sq ft. Step by step:

1. Area. All surfaces added up, minus the openings. If the openings are bigger than the surfaces, the area stops at zero.
2. Waste. We add an allowance for cuts and breakage, 10% unless you change it.
3. Tiles. Area with waste ÷ area of one tile with its joint, rounded up. Never less than one tile, even on a tiny shelf.
4. Boxes. Tiles ÷ tiles per box, rounded up. The box label gives the piece count and the square footage it covers.

The waste allowance depends on the layout. Tile Mountain, a UK tile retailer, suggests 10% for a straight lay and 15% for diagonal or herringbone, and keeping 5-10% of the order as spares. Many installers go to 20% for herringbone in a small room. The waste field is with the main inputs, so set it before you look at the box count.

On narrow walls with large tile, area alone falls short: every cut row uses up a whole tile, even if you only need a strip of it. So the calculator also counts the actual layout, row by row, and keeps the higher number. Take an 18 in wide, 7 ft tall strip beside a shower in 12 × 24 in tile: the area with 10% waste says 6 tiles, but every row needs its own cut piece, so the calculator says 7. In metric, a wall 70 cm wide and 2 m tall in 60 × 60 cm tile comes to 5 tiles by area and 6 laid.

How much thinset or tile adhesive do I need?

For large floor tile such as 12 × 24 in, plan on about 1.25 lb of thinset per square foot (6 kg/m²); small wall tile needs about 0.6-0.8 lb (3-4 kg/m²). The total is area × consumption, and the consumption depends on the trowel notch, which sets the thickness of the bed. CUSTOM Building Products prints a coverage chart for its MultiSet thin-set: a 50 lb bag covers 85-95 sq ft with a 1/4 × 1/4 in square-notch trowel, and 60-67 sq ft with a 1/4 × 3/8 in notch. In the UK, where adhesive usually comes in 20 kg bags, Tile Mountain gives about 4-5 m² per bag with a 6 mm notch and 2.5-3.5 m² with a 10-12 mm notch.

In feet and inches the calculator starts at 1.25 lb per sq ft, which is 40 sq ft per 50 lb bag; in metric at 6 kg/m², about the same. That is more than CUSTOM's chart gives for the 1/4 × 3/8 in notch, because the default tile is large (12 × 24 in, or 60 × 60 cm in metric), and for large tile CUSTOM notes that you may need a bigger notch and back-troweling, which means spreading thinset on the back of the tile too. For small wall tile on a 1/4 in notch, lower it to 0.6-0.8 lb per sq ft (3-4 kg/m²) in the advanced options.

In imperial units we pick 50 lb bags and add a 10 lb bag only when what is left fits in it. In metric we do the same with 20 kg bags, the usual size in the UK, and 5 kg bags.

Grout calculator: how much grout do I need?

For 12 × 24 in tile, 3/8 in thick, with 1/8 in joints, you need about 0.049 lb of grout per sq ft, so a 25 lb bag covers about 513 sq ft. The calculator works it out with the formula European grout makers print on their data sheets:

kg/m² = (A + B) ÷ (A × B) × C × D × 1.6

A and B are the tile sides, C the tile thickness and D the joint width, all in millimetres; 1.6 is the density of the mixed grout in kg per litre. You can enter inches: the calculator converts.

Big tile needs little grout, because a square foot of it has only a few feet of joint. Sika's chart for SikaTile-800 Sanded Grout gives 525 sq ft per 25 lb bag for the same 12 × 24 × 3/8 in tile, so the formula and the chart agree within 3%. On 2 × 2 in mosaic tile the same joint takes many times more grout.

In imperial units we pick 25 lb bags and 10 lb boxes; in metric, 5 kg and 2 kg bags. Joint width and tile thickness are in the advanced options.

Spacers and trim

Spacers are an estimate for a grid layout: one per tile, since every cross is shared by four tiles. We count them in packs of 200. A running bond or brick pattern makes T joints and uses more, and so does spacing tile off the wall at the edges. Mosaic sheets on mesh need no spacers, so for 2 × 2 in mosaic and anything smaller the list leaves them out.

Trim (edge profile) goes on outside corners and where tile stops partway up a wall. Enter the length of those edges in the advanced options and the calculator counts the bars: 8 ft in imperial, 2.5 m in metric, rounded up. We do not add anything for 45 degree miter cuts at the corners, so if you have a lot of them, add about 2 ft per corner.

A worked example

In feet and inches (US). The calculator opens with a 12 × 10 ft bathroom floor, 12 × 24 in porcelain tile 3/8 in thick, 8 tiles per box, 1/8 in joints, 10% waste, thinset at the default 1.25 lb per sq ft.

• Area: 12 × 10 = 120 sq ft
• Tiles: 120 × 1.10 ÷ 2.03 = 64.98, so 65 tiles
• Boxes: 65 ÷ 8 = 8.1, so 9 boxes (72 tiles, 144 sq ft)
• Thinset: 120 × 1.25 = 150 lb, so three 50 lb bags
• Grout: about 5.9 lb, so one 10 lb box

In metres (UK and elsewhere). In metric it opens with a 4 × 3 m floor, 60 × 60 cm tile 9 mm thick, 4 tiles per box, 3 mm joints, adhesive at 6 kg/m² and 10% waste.

• Area: 12 m², tiles 12 × 1.10 ÷ 0.3636 = 36.3, so 37 tiles and 10 boxes
• Adhesive: 12 × 6 = 72 kg, four 20 kg bags
• Grout: 12 × 0.144 = 1.73 kg, one 2 kg bag

Visitors in the US see the calculator in imperial units, everyone else in metric. You can switch at any time.

Common mistakes

• Buying boxes on different days. Different production runs can differ in shade and size, even under the same product code. Buy everything at once and check that the lot number matches on every box.
• Keeping no spares. A tile that cracks in five years can only be replaced with one from the same batch. Keep a few pieces, or a full box.
• Using too small a trowel on large tile. It leaves voids under the tile, which then sounds hollow or cracks. Use a bigger notch, back-trowel, and raise the thinset per square foot.
• Forgetting niches and window returns. Small areas, but almost all cuts.

When to call a tile setter

Call a professional tile setter (a tiler in the UK) if the subfloor is out of flat or cracked, if a curbless shower needs waterproofing, if you are setting tile larger than 24 × 48 in or thin porcelain panels, or if there is radiant floor heating underneath, which needs the right thinset and movement joints. A herringbone or diagonal layout in a room that is out of square is also a job for experienced hands.

These estimates do not replace the data sheets. When in doubt, follow the instructions of the thinset, grout and tile you buy.