Tile Calculator

This tool estimates the number of tiles needed to cover a floor, roof, wall or any other surface. It accounts for the gap or overlap between tiles, which is what separates a usable estimate from a rough one.

Enter the tile size, the area to cover as either dimensions or a total, and the grout gap. Add a box quantity and a price and it returns boxes and cost as well, along with the range you should actually order.

How the count is worked out

Each tile does not occupy its own size on the finished surface. It occupies its size plus one gap, because every tile carries a grout line along two of its edges. A 12 cm tile with a 0.25 cm gap therefore takes up 12.25 cm of floor in each direction.

The count is the area to cover divided by that effective footprint, rounded up. For 20 by 15 metres, that is 3,000,000 square centimetres divided by 150.0625, which comes to 19,991.7 and rounds to 19,992 tiles. Boxes follow from dividing by the tiles per box and rounding up again.

Leaving the gap out of that calculation looks harmless and is not. The same room with the gap ignored needs 20,834 tiles, an overestimate of more than 800, and the error grows the smaller the tile gets because the grout line becomes a larger share of each footprint.

Gap size

Floor and wall tiles are normally laid with gaps between them. Tiles that look identical are rarely uniform in shape and size, and laid tight against each other they will not sit true. The gaps are filled with grout, which is why they are often called grout lines or grout size.

Grout is a form of concrete, and the gap between tiles ranges from about one sixteenth of an inch to half an inch, roughly 1.6 mm to 12.7 mm. Tile size, material and the look you are after all affect the choice.

Small gaps are harder to work with when tiles are not perfectly uniform. Rectified tiles, which are processed after firing so every piece is the same size, allow tighter spacing at additional cost. More uniformly cut materials such as granite also take smaller grout lines, which makes the joints less visible.

In some cases the tiles overlap rather than sitting apart. Roof tiles and wood siding are laid this way so water runs off rather than through. The calculator handles both: a positive gap for spacing, a negative value for an overlap.

An overlap increases the tile count for the same area, because each piece covers less than its own size. Setting a 1 cm overlap on the example above raises the requirement from 19,992 to 24,794 tiles, which is a quarter more material and worth knowing before ordering rather than after.

Why order more than the calculation says

The calculator suggests 5% to 10% above the bare count, and both ends of that range exist for reasons.

Cutting waste. Rooms are rarely a whole number of tiles across. Every edge produces an offcut, and the piece cut away is usually unusable. A long narrow room has more perimeter per square metre than a square one, so it wastes more.

Breakage. Tiles chip on the saw, on the way in, and occasionally underfoot.

Future repairs. This is the one people skip and regret. Dye lots vary between production runs, so a tile bought two years later will rarely match, even with the same product code. A box put aside in the loft is cheap insurance against one cracked tile in the middle of a floor.

Go to the top of the range, or beyond it, for diagonal and herringbone layouts, for rooms with many corners or alcoves, and for large-format tiles where a single bad cut wastes a lot of material.

Tile installation options

Size

Tile sizes run from small mosaics around 3/8 of an inch up to slab tiles of 24 by 48 inches, with everything in between. Square tiles, with matching width and length, are the most popular, the most widely available and the easiest to lay.

Straight-edged tiles, whether rectangular, square or parallelogram, are the common case. Unusual shapes exist and are harder to install.

Large tiles make a small room look bigger, more open and cleaner, because there are fewer grout lines to break up the surface. The trade-off is waste: every cut into a large tile discards more material. Smaller tiles waste less and add texture, at the cost of far more grout line and a longer job.

Material

Ceramic and porcelain are the most cost-effective and come in the widest range of styles. Porcelain is denser and absorbs less water, which makes it the better choice for wet areas and outdoors.

Glass tiles are visually striking but crack under pressure, so they are not suitable for floors. They are most often used for kitchen and bathroom backsplashes.

Quarry tiles have rough surfaces that give grip, which suits floors that get wet or greasy. They are common outdoors and in restaurant kitchens.

Stone, including marble and granite, gives natural patterns, textures and colours that ceramics struggle to imitate, and tends to blend into the grout edges for a more uniform overall look.

Layout pattern

The most common layout is a linear grid of square or rectangular tiles, or the same grid turned 45 degrees into a diamond.

Running bond layouts offset each row like brickwork, usually at a 2:1 length to edge ratio. They generally use about 10% more material than a straight grid, because every row starts with a cut tile.

Herringbone lays tiles at angles, normally 45 or 90 degrees. Like running bond it uses more material than a linear layout, and rather more of it, since both ends of every row need an angled cut.

Whichever pattern you pick, the calculator counts the area rather than the arrangement, so add the pattern allowance on top of the 5% to 10% rather than instead of it.

Measuring the area to tile

The area to cover is rarely the same as the area of the room, which is why the calculator takes a total as well as dimensions.

For a floor, measure the room, then subtract anything the tiles do not run under: fitted units, a kitchen island, a bath panel, a hearth. Add any doorway recesses and threshold strips that do get tiled. Tiling under appliances is a judgement call, though running the tile through means a dishwasher can be replaced later without a visible edge.

For a wall, work one wall at a time and add the results, since walls in the same room are seldom the same size. Subtract windows and doors, but leave in anything below about a quarter of a square metre; the offcuts around a small opening usually cannot be used elsewhere.

For an irregular room, split it into rectangles, work out each one and add them together, then enter the sum in the total area field. That is faster than trying to average a shape and gives an answer you can check.

Common mistakes

The first is measuring the room instead of the surface. Fitted units, a bath, a kitchen island or a hearth all reduce the tiled area, and a doorway recess or a windowsill adds to it.

The second is mixing units without noticing. A tile quoted in inches on a floor measured in metres is fine here, since each field carries its own unit, but it is worth checking that the gap is in the unit you think it is. A gap entered as 0.25 inches rather than 0.25 cm changes the count noticeably.

The third is buying exactly what the calculator says. It returns the tiles required to cover the area, not the tiles required to finish the job.

The fourth is ordering in tiles when the shop sells in boxes. Boxes only come whole, which is why the calculator rounds them up, and why the box figure is usually the one to take to the counter.