How the tile calculator works
There are two tabs:
- Tiles, grout and thinset: enter the size of the floor or wall and the tile. It tells you how many tiles and boxes to buy, how much grout, and how many bags of thinset.
- Edge cuts and centring: enter the distance between two walls and the tile size. It shows how big the cut tile at the end will be, and warns you if it would be a thin sliver.
How many tiles do I need?
Multiply the length by the width, subtract anything that will not be tiled, such as a tub, and divide by the area of one tile plus its grout joint. Then add extra for cuts and breakage. The more complicated the layout, the more you waste:
| Layout | Extra to buy |
|---|---|
| Straight grid | 10% |
| Offset or brick | 12% |
| Diagonal | 15% |
| Herringbone | 20% |
Tile is sold in boxes, so the calculator rounds up to a whole box. Buy everything at once, since the colour and size of a tile can vary between batches, and keep a few spare tiles for repairs.
How much grout do I need?
Grout fills the joints, so the amount depends on the joint width, the thickness of the tile, and the size of the tile. Small tiles have many more joints than large ones, so a mosaic needs far more grout per square foot than a 24 in tile. The calculator works out the volume of the joints and adds 15% for waste and clean-up.
Use unsanded grout for joints narrower than 1/8 in and sanded grout for wider ones. Epoxy grout is stain resistant but harder to work with.
How much thinset do I need?
It depends on the size of the notches in your trowel, which depends on the size of the tile. A bigger tile needs a deeper trowel and more thinset. The calculator uses these typical figures for a 50 lb bag:
| Trowel | Used for | Coverage per bag |
|---|---|---|
| 3/16 in V-notch | Mosaics and small tile | about 110 sq ft |
| 1/4 × 1/4 in square | Tiles under 8 in | about 95 sq ft |
| 1/4 × 3/8 in | 12 in tiles | about 70 sq ft |
| 1/2 × 1/2 in | Large format, 15 in or more | about 45 sq ft |
The bag of thinset will say what it covers, so check it. The result also depends on the flatness of the surface, because an uneven floor needs more.
Avoid thin edge cuts
If you start at one wall and tile across, whatever is left over becomes the cut tile against the other wall. Sometimes that is a thin strip of an inch or two, which is hard to cut, breaks easily and looks poor. Here is the fix:
- Divide the distance between the walls by the tile size plus the joint. The whole number is the number of full tiles.
- Look at the leftover. If it is under about 2 in, or less than a third of a tile, centre the layout instead.
- To centre it, use one fewer full tile, and cut the first and last tile in each row to half of the leftover plus a tile.
Do this for both directions of the room. Most people also start from the centre of the room, or from the most visible line, such as the doorway.
Worked examples
A 10 × 8 ft floor, 12 in tiles
The floor is 80 sq ft. A straight layout adds 10%, so you need 87 tiles. With 15 tiles in a box that is 6 boxes. You need about 6.6 lb of grout, which is a single 25 lb bag, and 2 bags of thinset with a 1/4 × 3/8 in trowel.
A room 10 ft across, 12 in tiles, 1/8 in joints
You get 9 full tiles and a cut of about 10 7/8 in, which is a good size.
A room 123 in across, same tiles
You get 10 full tiles and a 1 3/4 in cut, which is too thin. Use 9 full tiles and cut a tile of about 6 7/8 in at each wall.
Common mistakes
- Not planning the layout. Dry lay a row first, so you find the thin cuts before the thinset goes down.
- Using the wrong trowel. Large tiles on a small trowel leave voids, and the tile can crack.
- Skipping the prep. The surface should be clean, flat and firm. Fix any dips before you start.
- Mixing batches. The tone and size can vary, so buy it all at once.
- Not sealing. Natural stone and unglazed tile, as well as cement grout, need sealing.
Tips
- Use tile spacers so the joints stay even.
- Mix tiles from several boxes as you lay them.
- Use a wet saw for porcelain, and wear eye protection.
- Wait the time on the bag before you grout, usually 24 hours.
- Buy the trim, the edge profiles and the sealer at the same time.
