Tile Calculator: How Many Tiles, Plus Thinset and Grout
Give it the area and the tile size and it counts the tiles the way the floor does, tile plus joint, not tile alone. It also works out the thinset, the grout and the backer board, because those are the three things that send people back to the store on a Saturday.
When the figures look right, the tile material list downloads as a real PDF with your business details on it, built inside your own browser. Nothing you type is uploaded anywhere.
Worked example
These are the figures the calculator opens with and the answer it gives. Change anything above and every number below moves with it.
- Area to tile120 sq ft
- Tile width12 in
- Tile length24 in
- Tile thickness0.375 in
- Grout joint0.125 in
- Tiles per box8 each
- Waste allowance10 %
Tiles needed65 tiles
Anything 15 inches or longer counts as large format. The substrate has to be flat inside an eighth of an inch over ten feet, the notch goes up to half by half, and every tile gets back buttered for coverage. Offset the joints by a third at most, because a running bond half offset on a long plank telegraphs every bit of tile warp as lippage.
| Area with 10% waste | 132 sq ft |
|---|---|
| Coverage of one tile | 2.031 sq fttile plus one joint |
| Tiles per square foot | 0.49 |
| Boxes at 8 per box | 9 |
| Thinset, 50 lb bags | 4about 40 sq ft per bag at this tile size |
| Grout | 6.1 lbsold in 10 and 25 lb boxes |
| Backer board, 3 by 5 sheets | 8 |
The material list this produces
| Tile, boxes | 9 |
|---|---|
| Thinset mortar, 50 lb bags | 4 |
| Grout, lb | 7 |
| Tile spacers, each | 130 |
| Cement backer board, 3 x 5 sheets | 8 |
| Backer board screws, each | 320 |
What this calculator assumes
- The tile count is worked out from the space one tile actually occupies, which is the tile plus one grout joint on two sides, not the tile on its own. On a 12 by 24 with an eighth inch joint that difference is about one percent, and on a mosaic it is far more.
- 10 percent waste suits a straight lay in a square room. A diagonal or herringbone lay wastes 15, and a room full of jogs, niches and closets can reach 20.
- Grout is figured geometrically: the joint volume is the space around each tile times the tile thickness, converted at 105 pounds per cubic foot, which is where sanded grout lands once mixed. Manufacturer coverage charts vary, so treat this as the order quantity and not the gospel.
- Thinset coverage follows the trowel, and the trowel follows the tile: about 85 sq ft from a 50 lb bag with a quarter inch notch under small tile, 60 under 12 inch, and 40 under large format where the notch grows and the tile gets back buttered.
A tile is bigger than it says on the box
A 12 by 24 tile does not occupy two square feet of floor. With an eighth inch joint it occupies 12.125 by 24.125, which is 2.03 square feet, and that one percent is the difference between ordering enough and ordering nearly enough.
On large tile the effect is small and on small tile it is not. A one inch mosaic with a sixteenth joint gives up six percent of the floor to grout. Count the tile without the joint and you will be a box and a half short on a bathroom.
This calculator builds the count from the cell, the rectangle one tile plus one joint occupies, which is how the floor is actually filled.
Waste is about the layout, not the room
Ten percent is the number for a straight lay in a room with four square corners. Every cut at a wall produces an offcut, and on a straight lay about half of those offcuts start the next row.
A diagonal lay throws away both ends of every perimeter tile, so it wants fifteen. Herringbone is worse again. A room with a closet, a niche, a doorway jog and a tub deck is fifteen even on a straight lay, because the cuts stop repeating and nothing fits anywhere twice.
Buy the whole job at once. Tile is fired in batches and the shade moves between them, so a single replacement box next spring will look like a patch from across the room.
Thinset follows the trowel and the trowel follows the tile
Coverage on a bag of thinset is a function of notch size, and notch size grows with the tile. A quarter by quarter square notch under a small tile stretches a 50 pound bag across most of 85 square feet. Under a 12 inch tile you are at a quarter by three eighths and about 60. Under large format you are at half by half, back buttering as well, and you will be lucky to see 40.
The calculator picks the coverage from the tile size you enter, which is close enough to order by. Your bag will state its own figure and that is the one that governs.
Grout here is worked out geometrically rather than read off a chart: the volume of the joints around every tile, times the tile thickness, converted at 105 pounds per cubic foot. It is why the number moves when you change the thickness, and it is why a thick porcelain plank drinks more grout than a thin ceramic one at the same joint width.
Questions people ask
How many 12x24 tiles do I need for 100 square feet?
About 50, plus waste. One 12 by 24 with a normal eighth inch joint covers 2.03 square feet of floor, so 100 square feet takes 49.3 tiles, and at 10 percent waste you are buying 55, which is seven boxes of eight.
How much grout do I need per square foot?
It depends on the tile size, the joint width and the tile thickness, which is why the number here changes with all three. As a feel for it, a 12 by 24 at an eighth of an inch runs about 0.05 pounds a square foot, and a small mosaic can be five times that.
How much waste should I add for tile?
Ten percent for a straight lay in a simple room, fifteen for a diagonal or a cut up bathroom, twenty for herringbone. Under ten is optimistic anywhere, because a bad box and a few broken tiles will eat it.
Do I need backer board under tile?
On a floor over plywood, yes, or an uncoupling membrane instead. The calculator figures cement board in 3 by 5 sheets, which is the common size, and adds the screws. Over concrete you usually tile direct once it is flat and clean.
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Common sizes, worked out
The same calculator with the numbers already filled in, one page per size, each ending in its own material list.