Tile Calculator

Tile Calculator: How Many Tiles Do I Need?

Tiles are sold by the box, but rooms are measured by the square foot, and the two numbers rarely line up neatly. If you are asking how many tiles do i need, you need more than the room area divided by the tile area: the grout gap changes the area each tile covers, the layout changes how many tiles are cut and wasted, and grout and thinset have to be bought as well. This page works all of that out in imperial or metric units and shows every formula it uses.

Quick answer

For 100 sq ft, a 12 × 12 in tile needs 100 tiles before waste, ignoring the grout gap. The table below gives the same figure for the common sizes. Each count is simply 100 sq ft divided by the area of one tile, with nothing added for cuts, breakages or waste, and with the grout gap ignored — the calculator below puts the gap and the waste back in.

Tile size	Tiles needed per 100 sq ft
4 × 4 in	900
6 × 24 in plank	100
12 × 12 in	100
12 × 24 in	50
18 × 18 in	45 (44.4)
24 × 24 in	25

Check a row by hand: a 24 × 24 in tile covers 4 sq ft, so 100 ÷ 4 = 25 tiles. An 18 × 18 in tile covers 2.25 sq ft, so 100 ÷ 2.25 = 44.4, which rounds up to 45 tiles — you cannot buy part of a tile.

How the calculation works

The calculator follows the same steps a tiler works through on paper, in the same order, so you can check any result yourself with a pocket calculator.

• Effective tile area: (tile length + grout gap) × (tile width + grout gap). This is the area one laid tile actually covers, grout joint included.
• Tiles needed (net): area to tile ÷ effective tile area, rounded up, because you cannot lay part of a tile across a whole space.
• Tiles to buy: tiles net × (1 + waste percentage), rounded up. The waste percentage comes from the layout you choose, and you can edit it.
• Boxes: tiles to buy ÷ tiles per box, rounded up to a whole box.
• Grout estimate: area in sq ft × a factor for the tile size × (gap in inches ÷ 0.125). The factor is 0.20 for a longest side up to 6 in, 0.13 up to 12 in, 0.10 up to 18 in, and 0.085 for 24 in and above, giving grout in lb.
• Grout bags: grout in lb ÷ 25, rounded up. In metric, the area is still converted to sq ft for the estimate, then the grout is shown in kg and divided by 10 kg per bag.
• Thinset bags: area ÷ coverage per 50 lb bag, rounded up. The default coverage is 85 sq ft per bag, and you can change it.

Why does the grout gap slightly reduce the tile count? Because each tile in a finished floor effectively occupies its own area plus one grout joint — the joint on one side of it, since the joint on the other side belongs to the next tile along. A 12 in tile with a 1/8 in gap therefore covers as much floor as a 12.125 in tile would on its own. The effect is small, and wider gaps make it slightly bigger, but over a whole room it can save a tile or two, which is why the calculator includes the gap instead of ignoring it.

Waste differs by layout because of cuts. In a straight grid most cuts are straight lines along the edges, and many offcuts can be used to start the next row. Turn the same tiles to 45 degrees for a diagonal layout and every edge becomes a series of angled cuts, with offcuts that rarely fit anywhere else. Herringbone and other complex patterns add still more angled cuts and more chances to miscut a tile, so they carry the highest allowance.

Dye-lot warning: buy all your tiles in one order, from the same production lot. Tile colour is set during firing, and shade can vary noticeably between lots, even for the same named product. A box bought months later to finish a job can stand out against the rest of the floor. For the same reason, keep a spare box after the job is done — a tile bought next year to replace a cracked one may not match, but a spare from the original lot will.

Worked example

Take a 10 × 12 ft bathroom floor tiled with 12 × 12 in tiles, a 1/8 in grout gap, and a straight layout at 10% waste. Here is every step, using the same formulas as the calculator above.

• Step 1 — area: 10 ft × 12 ft = 120 sq ft.
• Step 2 — effective tile area: 12.125 × 12.125 in = 1.021 sq ft.
• Step 3 — tiles net: ceil(120 ÷ 1.021) = 118 tiles.
• Step 4 — tiles to buy: ceil(118 × 1.10) = 130 tiles.
• Step 5 — boxes: 130 ÷ 10 tiles per box = 13 boxes.

Set the calculator to 10 × 12 ft, 12 × 12 in tiles, a 1/8 in gap and the straight layout, and it returns exactly 118 tiles net, 130 to buy and 13 boxes, matching the steps above.

Waste by layout

Use these figures as a starting point, then adjust for the room in front of you. The calculator sets the waste percentage from the layout you pick — 10% for straight, 15% for diagonal and 20% for herringbone / complex — and leaves the field editable so you can use a figure inside a range instead.

• Straight grid: 10%.
• Offset / brick bond: 10–15%, depending on how well the offcuts reuse.
• Diagonal: 15%.
• Herringbone: 15–20%.

Small rooms and rooms with many corners push every figure up: there is more edge per square foot, so more tiles are cut, and a mistake costs a bigger share of the total. Large-format tiles, 24 in and over, often need a few extra for breakage as well — each tile covers so much area that one broken or miscut tile is a large loss, and big tiles are easier to crack while handling and cutting.

Measuring tips

Good numbers in, good numbers out. Most tile shortages are measuring mistakes, not arithmetic mistakes, so measure each surface the way it will actually be tiled.

• Floors: measure the full room. Tiles normally run under appliances and into cupboards, so do not deduct the space those things stand on.
• Walls: measure each wall separately, then subtract the area of windows and doors that will not be tiled.
• Showers and splashbacks: measure each surface separately — each shower wall, the shower floor, each splashback run — and add them together before you calculate.
• Round up: always round measurements UP to the next half inch before entering them. Rounding down saves nothing and can leave you a tile short at the far wall.

Tile guides

Two short guides go deeper on the counting method behind this calculator — one works through tile counts by size and room, and the other is written for floors in both square feet and square metres.

• How Many Tiles Do I Need?
• Tile Calculator for Floors — Square Feet and m²

Frequently asked questions