Tile Area Calculator

A tile area calculator is the single most useful tool for stopping the two classic DIY tiler mistakes: buying a stack of tiles you do not need and cannot return, and buying too few tiles and having to abandon a Saturday afternoon to drive back to the trade counter for one more box. Type the dimensions of the floor (or wall) you are tiling, the size and orientation of the tile, and any doors or windows you want to subtract, and this calculator tells you exactly how many tiles and boxes to buy, with a sensible waste allowance and a tile-plan grid that shows how many whole tiles fit without any cutting. The default 10% wastage is the standard trade allowance for a straight grid layout; brick-bond, diagonal, and herringbone patterns stack their own pattern multiplier on top of your wastage slider, so a herringbone kitchen floor on a 20% waste allowance really means a 40% effective multiplier over the bare floor area.

Tiles are sold by the box in most countries, and the box-coverage in m² printed on the side of the box is the single number you need to convert the calculator's "effective area" output into a count of boxes. A standard 600 × 600 mm porcelain box from a UK trade supplier covers about 1.44 m² (four tiles of 0.36 m² each), a 300 × 300 mm ceramic box covers about 1 m² (eleven tiles of 0.09 m² each), and a 200 × 200 mm mosaic box covers about 1 m² (twenty-five tiles of 0.04 m² each). The calculator's default 1 m²/box works for the smallest formats and under-counts the larger ones, so set the box-coverage field to whatever the side of your box actually says.

How to Use the Tile Area Calculator

1. Pick the unit system, metric (metres, millimetres, square metres) or imperial (feet, inches, square feet). The calculator converts internally so the math is identical regardless of which is chosen.
2. Choose the surface you are tiling, Floor, Walls, or Floor + Walls. Floor + Walls gives you a single combined total tiles and boxes readout at the bottom of the results.
3. Pick the floor plan shape, Rectangle, L-shape, or Rectangle with bay. For a rectangular room, enter the length and width. For an L-shape, enter the overall rectangle dimensions and the cut-out rectangle dimensions in one of the four corners. For a room with a chimney-breast bay, enter the main rectangle and the bay protrusion and width, and pick which wall the bay sits on.
4. Enter the wall dimensions if you opted for Walls or Floor + Walls, wall height, wall width, and the number of identical walls. For a rectangular room, enter the height once and the width once, with a count of 4.
5. Enter the door and window dimensions as height, width, and count. Each opening is multiplied by its count and subtracted from the gross floor (or wall) area. Set the count to 0 if you have no doors or no windows.
6. Pick a tile size preset, 200 × 200 mm, 300 × 300 mm, 400 × 400 mm, 600 × 600 mm, 600 × 300 mm, or 600 × 1200 mm, or pick Custom and type any length and width in millimetres. Millimetres is the universal tile-sizing unit regardless of country, so the tile-size field is always millimetres.
7. Choose the orientation / pattern, Grid (stack bond, 1.00×), Brick-bond (½ offset, 1.05×), Diagonal (45°, 1.15×), or Herringbone (1.20×). The multiplier stacks on top of your own wastage slider.
8. Pick the lay direction, Horizontal or Vertical, for the tile-plan grid readout. This affects only the cut plan, not the count.
9. Set the grout gap in millimetres. The default is 3 mm, which is the most common residential gap for ceramic floor tiles. Rectified porcelain typically uses 2 mm; hand-made or rustic tiles typically use 4 to 6 mm.
10. Set the wastage allowance with the slider. The default is 10%, which is appropriate for a straight grid on a rectangular room. Diagonal typically needs 15%, herringbone typically needs 20%, and a beginner's first room typically needs 15% to 20% because of mis-cuts and breakages.
11. Set the box coverage in m²/box (or ft²/box in imperial). The default is 1 m²/box, which is correct for the smallest formats; larger formats typically come in 1.2 to 1.5 m² boxes.
12. Read the result box for the gross and net floor (or wall) area, the effective area after waste and pattern multipliers, the number of tiles to buy (rounded up because you cannot buy a third of a tile), and the number of boxes to buy. The tile-plan grid below shows the number of whole tiles that fit without cuts, plus the leftover partial tiles that fit only along the last row or column.

The whole calculator runs in the browser. For the Tile Area Calculator, Inputs are not stored, not transmitted, and not associated with any account.

The Formula

The single closed-form formula that drives the result box is:

net_m² = surface_area − Σ(opening_height × opening_width)

Then:

effective_m² = net_m² × (1 + waste_fraction) × pattern_multiplier

And:

tiles_to_buy = ceil(effective_m² / tile_area_m²)

Both directions work in any consistent unit. The tile-area conversion uses millimetres everywhere because millimetres is the universal tile-sizing unit worldwide; the room-area conversion uses metres (or feet in imperial mode) and converts to m² internally so the division by tile_area_m² is consistent. The conversion factors between metric and imperial are exact by international definition: 1 ft = 0.3048 m (NIST SP 811), 1 ft² = 0.09290304 m² (exact).

The pattern multiplier is applied multiplicatively on top of the wastage slider. A straight grid on a 10% waste allowance means effective = 1.10 × net. A herringbone on a 20% waste allowance means effective = 1.20 × 1.20 = 1.44 × net. A diagonal on a 15% waste allowance means effective = 1.15 × 1.15 = 1.3225 × net. This is the trade rule, codified by the British Ceramic Confederation and the Tile Association (UK), and reflects the empirical observation that each pattern produces a different mix of off-cut shapes, diagonal and herringbone produce more triangular off-cuts than square ones, and triangular off-cuts are harder to reuse on the next row.

Worked Examples

Example 1: 3 × 3 m bathroom floor, 600 × 600 mm porcelain grid, 10% wastage, 1 door. Gross floor area = 3 × 3 = 9 m². Subtract 1 door (0.9 × 2 = 1.8 m²) and 0 windows. Net floor area = 9 − 1.8 = 7.2 m². Effective area = 7.2 × 1.10 × 1.00 = 7.92 m². Tile area = 0.6 × 0.6 = 0.36 m². Tiles to buy = ceil(7.92 / 0.36) = ceil(22) = 22 tiles. At 1 m²/box, boxes to buy = ceil(7.92 / 1) = 8 boxes (or 6 boxes at 1.44 m²/box from a real trade supplier).

Example 2: 4 × 3 m bathroom floor plus walls, 600 × 300 mm brick-bond ceramic, 12% wastage, 1 door, 1 window. Gross floor area = 4 × 3 = 12 m². Subtract 1 door (1.8 m²) and 1 window (0.9 × 0.6 = 0.54 m²) = 2.34 m² deductions. Net floor area = 9.66 m². Gross wall area = 4 × (4 × 2.4) = 38.4 m². Same deductions. Net wall area = 38.4 − 2.34 = 36.06 m². Effective floor = 9.66 × 1.12 × 1.05 = 11.36 m². Effective wall = 36.06 × 1.12 × 1.05 = 42.41 m². Combined effective = 53.77 m². Tile area = 0.6 × 0.3 = 0.18 m². Total tiles = ceil(53.77 / 0.18) = ceil(298.7) = 299 tiles.

Example 3: 5 × 5 m kitchen floor, 600 × 600 mm porcelain grid, 10% wastage, no door deduction (open plan). Gross floor area = 5 × 5 = 25 m². No deductions. Effective area = 25 × 1.10 × 1.00 = 27.5 m². Tile area = 0.36 m². Tiles to buy = ceil(27.5 / 0.36) = ceil(76.39) = 77 tiles. Tile-plan grid: 5 / 0.6 = 8.33 → 8 columns; 5 / 0.6 = 8.33 → 8 rows; whole tiles = 8 × 8 = 64; partial tiles = 77 − 64 = 13.

Why Tile Estimates Go Wrong

The five classic tile-ordering mistakes are: (1) forgetting to add wastage, measure twice, order 10 to 15% more, throw the off-cuts away. (2) Mismeasuring the room and assuming square corners when the building is actually out of square by 20 mm, measure both diagonals, take the larger one. (3) Subtract-and-forget: subtracting doors and windows for a paint calculation but not subtracting them for the tile order, the tiles really are not going under the door. (4) Choosing the wrong metric, a 600 × 600 mm tile is not the same coverage as a 600 × 600 foot tile. (5) Ignoring the calibration tolerance, ceramic tiles vary by up to ±0.5% from their nominal size, and a 2 mm grout gap is the typical tolerance for rectified porcelain.

A sixth, less obvious mistake is forgetting to add a starter row. Most rooms have an alcove, a doorway, or a corridor that eats at least one row of full tiles off the back. If you measure the floor and order exactly the right number of tiles for the measured rectangle, you will come up short the moment you reach the alcove. The trade rule is to add a buffer row equal to one tile-length on every wall that meets another wall at less than 90°. The calculator's tile-plan grid surfaces this issue directly: the "partial tiles" count includes the off-cuts along the perimeter, but if your alcove cuts deeper than one tile-length you need to add it manually.

A seventh mistake is forgetting dye-lot variation. Tiles are glazed in batches called dye-lots, and each dye-lot is slightly different in colour and surface finish from the next. If you order the exact number of tiles from one dye-lot and then need to order more from a different dye-lot, the colour mismatch will be visible. Always check the dye-lot number on the side of the box before opening, and order all boxes from the same dye-lot if you have any choice.

Common Mistakes

The biggest single reason a DIY tile estimate is wrong is forgetting to add wastage. The trade rule is 10% for a straight grid, 15% for brick-bond, 20% for diagonal, and 25% to 30% for herringbone. These multipliers stack with your own wastage slider on the calculator. The second is underestimating the cut-tile count, every tile that crosses a corner, a doorway, or a fixed object (toilet, basin, radiator pipe) has to be cut, and cut tiles are wasteful because the off-cut is rarely reusable. The third is using the wrong tile size in the calculator, a 600 × 600 mm tile is 0.36 m² but a 600 × 600 cm tile would be 36 m². The fourth is forgetting to subtract the area under any fitted units, kitchen base units, bath tubs, shower trays, and fitted wardrobes are all areas you will not tile. The fifth is buying all the tiles from the same dye-lot, see the previous paragraph. The sixth is assuming the floor is rectangular when it is actually a slightly irregular trapezoid, measure both diagonals, take the larger one, and round up.

A seventh and final mistake is buying tiles with the wrong calibration grade. Tiles are graded by their dimensional tolerance: rectified porcelain (the most precise) varies by less than ±0.3% from the nominal size, standard porcelain varies by ±0.5%, and rustic or hand-made ceramic varies by ±1% to ±2%. If you buy a rectified porcelain floor tile and the room is actually out of square by 20 mm, every row will need a tapered cut to make the joints meet at the corners. The calculator does not model out-of-square rooms, but the tile-plan grid shows you how many whole tiles fit and how many partial tiles you will need to cut. If the partial-tile count is more than 30% of the total tile count, the room is significantly out of square and you should plan for more cuts.

Where Tile Calculators Show Up

Tile estimators are needed anywhere a surface will be covered with ceramic, porcelain, glass, stone, or mosaic. The most common use case is a DIY bathroom or kitchen renovation, where a homeowner needs to know how many boxes to order for a single floor or wall. Professional tilers use the same calculation to quote a job accurately so the customer is neither over-charged nor left with a half-box the tiler has to absorb. The calculator also handles shower walls (where every wall is the same height and the cut-outs are the shower valve and the showerhead), splashbacks (small rectangles behind a kitchen hob or a bathroom basin), outdoor patios (which need a slightly larger waste allowance for weather-related breakages), and commercial floors (which often need a more conservative waste allowance because of heavy foot traffic during installation).

For mosaic sheets, the calculator's mm input gives the per-tile size on the sheet (typically 20 × 20 mm, 25 × 25 mm, or 48 × 48 mm), and the box coverage should be set to whatever the sheet-pack actually covers in m², typically 1 m² per pack of 12 sheets. For natural stone, the calibration tolerance is wider than for porcelain, so the wastage slider should be at least 15% for a straight grid and 25% for a diagonal. For glass tiles, the breakage rate is much higher than for ceramic or porcelain, so the wastage slider should be at least 20% for a straight grid and 30% for a diagonal.

Frequently Asked Questions

How many tiles do I need for a 3 × 3 m bathroom floor? For a 3 × 3 m bathroom floor with 600 × 600 mm porcelain tiles in a straight grid, you need 28 tiles (or 22 if you subtract one standard 0.9 × 2 m door). The math: gross floor area is 9 m², deductions are 1.8 m² for one door, net area is 7.2 m², effective area at 10% wastage is 7.92 m², tile area is 0.36 m², tiles = ceil(7.92 / 0.36) = 22 tiles. Without the door deduction, 9 × 1.10 = 9.9 m² effective → ceil(9.9 / 0.36) = 28 tiles.

How many tiles per square metre? It depends on the tile size. 600 × 600 mm = 2.78 tiles per m² (1 / 0.36). 300 × 300 mm = 11.11 tiles per m² (1 / 0.09). 200 × 200 mm = 25 tiles per m² (1 / 0.04). 600 × 300 mm = 5.56 tiles per m² (1 / 0.18). 600 × 1200 mm = 1.39 tiles per m² (1 / 0.72). The calculator displays the tiles-per-m² figure as a "Tiles per m² (gross)" row in the results box.

How much wastage should I add? 10% for a straight grid (stack bond), 15% for brick-bond (½ offset), 20% for diagonal (45°), and 25% to 30% for herringbone. These are stacked on top of the wastage slider on the calculator, so a herringbone with a 20% wastage slider really means a 1.20 × 1.20 = 1.44× effective multiplier. For a beginner's first room, add an extra 5% to whatever pattern multiplier you choose.

What is the standard grout gap? 3 mm is the most common residential gap for ceramic floor tiles. 2 mm is the typical tolerance for rectified porcelain. 4 to 6 mm is typical for hand-made or rustic ceramic. 1 mm or less is typical for polished marble or glass mosaic. The grout gap affects only the visual result, not the tile count, so the calculator does not use the grout value in the math, it is included as a reference for the user.

Do I need to subtract doors and windows? Yes, if you are not tiling under them. A standard 0.9 × 2 m door is 1.8 m² and a standard 1.2 × 1.2 m window is 1.44 m². For a 3 × 3 m bathroom, a single door takes up about 20% of the gross floor area, which is a significant saving. The calculator subtracts the door and window area automatically based on the inputs you give it.

How do I tile an L-shaped room? Pick the L-shape floor plan option on the calculator. Enter the overall rectangle dimensions and the cut-out rectangle dimensions in one of the four corners. The calculator computes the L-shape area as the overall rectangle minus the cut-out. For a more complex L-shape (e.g., a T-shape or a U-shape), break the room into rectangles and add the calculator outputs together.

What is the difference between ceramic and porcelain tiles? Ceramic tiles are made from a red or white clay, fired at a lower temperature, and have a higher water absorption rate (typically 3% to 7%). Porcelain tiles are made from a denser clay, fired at a higher temperature, and have a lower water absorption rate (typically less than 0.5%). Porcelain is more durable, more stain-resistant, and more expensive. The calculator treats them identically for coverage purposes, the difference is in the per-box coverage, which the box-coverage input captures.

Can I use this calculator for a shower wall? Yes, switch to the Walls tab, set the wall dimensions to the shower wall height (typically 2.0 to 2.4 m) and width (typically 0.8 to 1.2 m), set the count to 1, and read the tiles to buy. If you are tiling all four shower walls, enter the average wall width and set the count to 4. The calculator handles L-shaped shower walls by switching to the L-shape floor plan option and reading the wall equivalent.

How accurate is the tile-plan grid? The tile-plan grid assumes a perfectly rectangular room with square corners. If the room is out of square by more than 20 mm, the cut-tile count will be higher than the calculator predicts. The trade rule is to measure both diagonals and take the larger one as the basis for the area calculation. The calculator gives you a useful starting estimate, but a real tiler would always plan for an extra row of cuts along the most out-of-square wall.

References

• British Ceramic Confederation (BCT), Trade guidance on ordering ceramic and porcelain tiles, including the standard 10% cutting-waste rule.
• The Tile Association (UK), Installation tolerance and pattern-waste guidance for brick-bond, diagonal, and herringbone layouts.
• ASTM C1067, Standard Practice for Conducting a Wear Test for Tile Installation, covering expected breakage and dye-lot variation.
• Trade Superstore & Marshall's guide, Typical 10% waste for a straight grid, 15% for diagonal, 20% for herringbone.
• Wikipedia "Tile" article, Tile sizes, dye-lot calibration, wastage conventions, and box-coverage standards.
• NIST Special Publication 811 (Guide for the Use of the SI Units), exact conversion factors: 1 ft = 0.3048 m, 1 ft² = 0.09290304 m².
• ISO 13006:2018, Ceramic tiles, Definitions, classification, characteristics and marking.
• EN 14411:2016, Ceramic tiles (European standard for tile dimensions and tolerances).