Tile Calculator
Enter the surface you are tiling and the size of your tile. You get the tile count with a cutting allowance, the number of boxes to buy, and how much thin-set mortar and grout goes with it.
How many tiles do I need?
Divide the square footage of the floor or wall by the square footage of one tile, then add a cutting allowance of 10 % for a straight lay or 15 % for a diagonal or herringbone lay. A 12 ft x 10 ft floor is 120 sq ft; in 12 in x 12 in tile, which is 1 sq ft each, that is 120 tiles plus 10 % overage, so 132 tiles.
Tiles you need
Enough tile for 120 sq ft including a 10 % cutting allowance.
- Area to cover
- 120 sq ft
- Tiles before waste
- 120
- Thin-set mortar
- 2 bags50 lb, 85 sq ft per bag
- Grout
- 1 bag8.1 lb, 25 lb bags
The numbers above are a worked example for a 12 ft x 10 ft floor in 12 in x 12 in tile. Allow this page to run scripts in your browser to use your own dimensions, or follow the formula further down the page and do it by hand.
How the tile calculator works, step by step
Every tile estimate is the same three-step chain: find the area you are covering, find the area of one tile, divide, then add a cutting allowance. The only place people go wrong is mixing inches and feet, which is why the tile size is entered in inches and everything else in feet.
There are 144 square inches in a square foot, which is where that 144 comes from. A 12 in x 12 in tile is exactly 1 sq ft. A 12 in x 24 in tile is 288 / 144 = 2 sq ft.
The result is always rounded up. There is no such thing as buying 146.3 tiles, and the last box is the one you need when a cut goes wrong on the final row.
Worked example: a 12 ft x 10 ft bathroom floor in 12 in x 12 in tile
- Area to cover: 12 x 10 = 120 sq ft
- Area of one tile: (12 x 12) / 144 = 1 sq ft
- Tiles before waste: 120 / 1 = 120 tiles
- With a 10 % straight-lay allowance: 120 x 1.10 = 132, rounded up to 132 tiles
- If the box covers 15.5 sq ft, that is 132 / 15.5 = 8.5, so 9 boxes
Change nothing but the pattern and the numbers move: a diagonal lay at 15 % gives 138 tiles, and the extra six tiles are exactly the corner triangles you cut and throw away.
Tile waste and overage: how much extra to buy
Overage, or waste allowance, is the extra tile you buy on top of the bare square footage. It is not padding: it is the material that physically ends up in the dumpster. Perimeter cuts, cuts around a toilet flange or a door jamb, tiles that break during scoring, and the pieces you keep spare for a future repair when that exact dye lot is discontinued.
| Situation | Allowance | Why |
|---|---|---|
| Straight or stacked lay, square room | 10 % | Perimeter cuts only |
| Diagonal, herringbone or chevron | 15 % | Every perimeter tile is cut twice |
| Rooms with alcoves, islands, many corners | 15 to 20 % | More edges, more cuts |
| Large format tile over 15 in on a side | 15 % | Each broken piece costs more square footage |
| Mosaic sheets | 10 % | Sheets can be cut between mesh lines |
A practical extra: whatever the calculator says, buy at least one full spare box and store it flat and dry. Tile is manufactured in batches with a dye lot number, and matching a lot two years later is usually impossible.
Thin-set mortar: how many bags
Mortar coverage depends on one thing above all: the notch size of your trowel. A deeper notch holds more mortar per square foot, so the same 50 lb bag goes less far. The figures below are the approximate coverages published for a standard polymer-modified thin-set.
| Trowel notch | Coverage per 50 lb bag | Typical use |
|---|---|---|
| 3/16 in V-notch | about 90 sq ft | Small wall tile, mosaics |
| 1/4 in x 1/4 in square | about 85 sq ft | Tile up to 12 in |
| 1/4 in x 3/8 in square | about 60 sq ft | 12 in to 16 in tile |
| 1/2 in x 1/2 in notch | about 35 sq ft | Large format, uneven substrates |
Coverage source: Custom Building Products, VersaBond Professional Thin-Set Mortar (TDS-119) - technical data sheet. Coverage varies with substrate flatness and technique. Always read the bag you actually buy: a large-and-heavy-tile mortar or a rapid-set product will not cover the same as a standard thin-set.
Two things the coverage table cannot know. If your substrate is out of flat, you will burn through mortar filling the low spots. And if you back-butter large format tile, which you should above 15 in, plan on roughly one third more mortar than the table says.
Grout: the formula nobody shows you
Most grout charts give you a table and no arithmetic. The chart works only for the exact tile sizes listed, which is useless the moment you buy a 6 in x 24 in plank. Here is the actual geometry, which works for any tile.
The idea is simple. One tile plus one joint on each side is a repeating module. The tile fills part of that module; the grout fills what is left, all the way down to the depth of the tile. Multiply the leftover fraction by 144 square inches and by the joint depth, and you have the cubic inches of grout in every square foot of floor. Dry sanded grout weighs roughly 105 lb per cubic foot, which converts that volume into pounds and then into 25 lb bags.
Worked example: 12 in x 12 in tile, 1/8 in joints, 3/8 in thick
- Module: 12.125 x 12.125 = 147.02 sq in
- Tile: 12 x 12 = 144 sq in
- Joint fraction: 1 - 144 / 147.02 = 0.0205
- Cubic inches per sq ft: 144 x 0.0205 x 0.375 = 1.108
- Pounds per sq ft: 1.108 / 1728 x 105 = 0.067 lb
- Over 120 sq ft: 8.1 lb, so one 25 lb bag
Grout density and bag size cross-checked against Custom Building Products, Polyblend Plus Sanded Grout (TDS-360) - technical data sheet. Manufacturer coverage charts assume full joints and no waste in the bucket; mix in batches you can use before the pot life runs out.
Note the direction of the numbers. Small tile with wide joints eats grout, and not by a little: 3 in x 6 in subway tile with 3/16 in joints needs about 0.287 lb per sq ft, while 24 in x 24 in tile with 1/16 in joints needs about 0.011 lb per sq ft. That is a factor of twenty-five for the same floor area. If you are setting mosaic, take the grout line seriously.
Cases the simple formula does not cover
Rooms that are not rectangles
Break the floor into rectangles, calculate each one, and add the areas. An L-shaped room is two rectangles. A room with a bay window is a rectangle plus a trapezoid, and a trapezoid is (base one + base two) / 2 x depth. Then switch this calculator to total square footage and enter the sum.
Circles and curves
Area of a circle is 3.1416 x radius squared, with the radius in feet. For a curved edge, take the bounding rectangle and do not subtract the offcut: on a curve you cut every tile on the arc, so the waste is real.
Walls and floors in the same room
Calculate them separately. Wall tile is usually thinner, is set with a smaller notch trowel, and often uses a different grout joint. Adding a 60 sq ft shower surround to a 40 sq ft floor and calculating once will give you the wrong mortar count even if the tile count happens to be right.
Do you subtract obstacles?
For a toilet flange, a floor drain or a kitchen island under about 6 sq ft: do not subtract. You will cut tile around it and the offcuts rarely serve elsewhere. For anything larger, such as a fixed cabinet run or a sunken tub, subtract the footprint and keep the waste percentage as it is.
Underlayment and movement joints
This calculator sizes tile, mortar and grout only. Uncoupling membrane, backer board, waterproofing and movement joint material are separate line items sold by the roll or the sheet, and industry guidance calls for movement joints in large floors and wherever tile meets a restraining surface.
Frequently asked questions
How many 12x12 tiles do I need for 100 square feet?
A 12 in x 12 in tile covers exactly 1 sq ft, so 100 sq ft needs 100 tiles before waste. Add the cutting allowance and you get 110 tiles at 10 % for a straight lay, or 115 at 15 % for a diagonal lay. If the box covers 15 sq ft, that is 8 boxes.
How many 12x24 tiles are in 100 square feet?
A 12 in x 24 in tile is 288 square inches, which is 2 sq ft. So 100 sq ft takes 50 tiles before waste, and 58 tiles with a 15 % allowance, which is the rate to use because plank sizes are usually laid in a running or herringbone bond.
Should I calculate in tiles or in boxes?
Buy in boxes, check in tiles. Box coverage differs between products even at the same nominal tile size, and stores sell full boxes only. Enter the coverage printed on the box in the optional field and the calculator converts your tile count into the number of boxes to put in the cart.
How much thin-set do I need for 100 square feet of tile?
With a 1/4 in x 1/4 in square-notch trowel, one 50 lb bag covers roughly 85 sq ft, so 100 sq ft takes two bags. Move up to a 1/4 in x 3/8 in notch for larger tile and coverage drops to about 60 sq ft per bag, so the same floor takes two bags with very little to spare.
Is 10 % waste enough for tile?
For a rectangular room laid straight, yes. Go to 15 % for diagonal, herringbone and chevron patterns, for large format tile, and for any room with alcoves or a lot of corners. Whatever the number, buy a spare box on top for future repairs, because dye lots change.
Does the calculator account for grout joints in the tile count?
Not in the tile count, and that is deliberate. Joints make each tile occupy slightly more floor, which very slightly reduces the number of tiles needed, by well under 2 % at normal joint widths. Ignoring it errs on the safe side. Joint width is used where it genuinely matters, in the grout quantity.
How many bags of grout for a 100 square foot floor?
It depends on tile size, joint width and tile thickness. A 100 sq ft floor of 12 in x 12 in tile with 1/8 in joints and 3/8 in thickness needs about 6.7 lb of grout, so one 25 lb bag. The same floor in 3 in x 6 in subway tile with 3/16 in joints needs roughly 29 lb, so two bags.