Tile Calculator

What the tile calculator does

Tiling is unforgiving on quantity. Run short and the next box may be a different shade; overbuy and tile is awkward and expensive to have spare. This works out the count properly. You give it the area, the tile size, the grout gap, and a waste figure, and it returns the tiles needed, the boxes, and a cost, with the area in your choice of square meters or square feet.

It is the most detailed of the surface calculators because tiling has the most moving parts. Below is how it works, including the two things most rough counts miss.

How to use it

1. Enter the area length and width, the surface you are tiling, each with its unit.
2. Enter the tile length and width, the size of a single tile.
3. Enter the gap size, the grout joint between tiles, and a waste percentage.
4. Add a box size and price if you want boxes and a cost, choose the output unit, then press Calculate, or Reset to clear it.

How the tile count is worked out

At heart it is the area of the surface divided by the area one tile covers:

Tiles = surface area ÷ area covered by one tile

The clever part is that the area covered by one tile includes its grout gap, which the next section explains. Once it has the raw count, the calculator adds your waste percentage, rounds up to whole tiles, then divides by the box size and rounds up to whole boxes. The cost is the boxes times your price.

How the grout gap changes the count

This is the detail rough counts miss. A tile does not sit flush against its neighbours; there is a grout joint between them. So on the floor, each tile really occupies its own size plus one grout gap in each direction, and the calculator builds that in by adding the gap to the tile's length and width before working out how much area it covers.

The effect is small but real: because each tile effectively covers a touch more than its bare size, you need slightly fewer of them than dividing by the plain tile area would suggest. On a big floor with wide grout lines that adds up to a tile or two, which is the difference between the grout being accounted for and not.

Setting the waste figure

The waste percentage is yours to set, and it is not padding; it covers the tiles you cut to fit. Around the edges of the room, and around fixtures, full tiles get cut down and the offcuts often cannot be used elsewhere. For a plain rectangular floor laid square, about 10 percent covers it.

Some layouts need more. A diagonal layout cuts every edge tile at an angle, and patterns like herringbone cut even more, so those climb toward 15 percent or beyond. Lots of corners, alcoves, and pipework push it up too. So set the waste to suit the layout, leaning higher for anything more complex than straight rows, and keep a few spare from the same batch for future repairs.

A worked example: an 80 sq ft floor

Say the floor is about 80 square feet, tiled with 12 inch tiles, a small grout gap, and 10 percent waste.

Bare, 80 square feet of 12 inch tiles would be 80 tiles. With the grout gap each tile covers a little more, trimming the raw count to about 78 tiles. Add 10 percent waste and it rounds up to roughly 86 tiles. If a box holds 10, that is 9 boxes.

So the grout gap nudges the count down a touch, and the waste pushes it back up, which is why both belong in the sum.

Questions people ask

How many tiles do I need?

Divide the surface area by the area one tile covers, including its grout gap, then add waste. An 80 square foot floor in 12 inch tiles works out to about 86 tiles with 10 percent waste.

Does the grout gap really matter?

A little. Each tile covers its own size plus a grout joint, so accounting for the gap means you need slightly fewer tiles. On a big floor with wide joints it is a tile or two.

How much waste should I allow?

About 10 percent for a plain floor laid square, and 15 percent or more for diagonal or patterned layouts, which cut more edge tiles.

How do I work out boxes?

Divide the tile count by how many tiles are in a box and round up. Enter the box size and the calculator does it, and gives a cost if you add a price per box.

References

A quick note on the numbers. The count is geometry, the surface area divided by the tile area including the grout joint. The waste guidance, around 10 percent for a straight layout and more for diagonal and patterned work, follows tiling installation practice as set out by the Tile Council of North America. The unit conversions follow the US National Institute of Standards and Technology guide.

1. Tile Council of North America (TCNA), tile installation and material allowance guidance. https://www.tcnatile.com
2. National Institute of Standards and Technology (NIST), Special Publication 811, Guide for the Use of the International System of Units (SI). https://www.nist.gov/pml/special-publication-811