Tile Calculator

Running short on tile is a special kind of pain. The store is closed, the thinset is already mixed, and the "same" tile you reorder next week arrives from a different dye lot — close enough that the box matches, different enough that you can see the line across your floor forever. This calculator keeps you out of that mess. Tell it your surface length and width, your tile size, and a waste allowance, and it divides the surface area by a single tile's area, adds waste for cuts and breakage, and rounds up to whole tiles. It handles floors, walls, and backsplashes in feet or meters, with tile sizes in inches or centimeters. Get the number right and you make one trip to Home Depot. Get it wrong and you're either driving back mid-project or storing four boxes of porcelain in the garage until your kids inherit them.

How to use this calculator

Measure the surface length at its longest point — old walls bow, so don't trust one corner. Use a tape measure and round up to the nearest inch.
Measure the width the same way. For walls, that's floor to ceiling; include the area behind the toilet or vanity even though tile gets cut around them.
Read the actual tile size off the box, not the shelf name. A tile sold as 12x12 often measures 11-7/8 inches, and the box's stated coverage in square feet is the number that matters.
Enter the tile's length and width separately. Most are square, but planks like 6x36 need both numbers to get the area right.
Set the waste allowance: 10% for a straight grid in a simple rectangular room, 15% for diagonal layouts, herringbone, or rooms with lots of cuts.
Press Calculate. The result already includes waste and rounds up, so it's the number of tiles to order — not the number that ends up on the surface.
Convert to boxes before checkout: divide the result by the tiles-per-box printed on the box and round up. Order full boxes — stores take unopened boxes back, not loose tiles.

Formula

The math is straightforward division. Surface area is length times width, and a single tile's area is tile length times tile width, with both converted to the same units first. Base tiles equal surface area divided by tile area — that's the count if every tile landed perfectly. Your order quantity multiplies that by one plus the waste percentage and rounds up, because cuts, chips, and breakage are guaranteed and partial tiles don't exist.

Worked example

Take a guest bathroom floor, 8 feet by 6 feet. The surface area is 8 × 6 = 48 square feet. You're using 12x12 inch ceramic tile — each tile is 144 square inches, which is exactly 1 square foot. Base tiles: 48 ÷ 1 = 48 tiles, the count for a perfect world with no cuts. Your bathroom is not a perfect world. There's a toilet flange to cut around and a doorway to notch, so set 10% waste: 48 × 1.10 = 52.8. The calculator rounds up — you can't buy eight-tenths of a tile — giving 53 tiles to order. If you fall in love with a diagonal layout at the store, bump waste to 15%: 48 × 1.15 = 55.2, which rounds up to 56 tiles. Either way, convert to boxes before checkout. If the box holds 10 tiles, 53 tiles means 6 boxes (60 tiles) — and yes, keep the 7 leftovers. They're your repair stock from the same dye lot, and future-you will be grateful when a dropped shampoo bottle chips a tile in 2029.

Measurement tips

Dry-lay one full row from the center of the room before you mix any thinset. It takes ten minutes and shows you exactly where the awkward sliver cuts land — you can shift the layout half a tile and make them disappear.
Check the caliber and shade codes on every box before you leave the store. Tile is fired in batches, and two boxes with different lot numbers can sit side by side on your floor like a before-and-after photo.
Rent the wet saw instead of buying one for a single bathroom. Home Depot rents them for around $60 a day, and a rental saw cuts straighter than the $90 special you'd buy and regret.
For large-format tile — anything 12x24 or bigger — buy a box of tile leveling clips (about $20 for a hundred on Amazon). They kill lippage, the edge-to-edge height difference that makes big tiles look amateur.
Keep your spare tiles from the same batch in the attic, not the garage. Ten years from now you want the exact dye lot, and the box will still be sitting there when you need it.
Mosaic sheets are sold by the square foot of the sheet, not the chip. Don't try to count the little squares — the box coverage number already accounts for them.
One 50-pound bag of thinset covers roughly 40–50 square feet with a 1/4-inch notched trowel. Buy the thinset on the same trip as the tile so the project can't stall on a missing bag.

Common mistakes

Subtracting the toilet footprint from the floor area, then running short. The square foot you "saved" under the toilet costs you three wasted tiles cutting the curve around the flange. Measure the full rectangle.
Using 10% waste on a diagonal or herringbone layout. Every angled cut throws away a triangle, and 15–20% is the real number — 10% leaves you one box short with the thinset already mixed.
Reordering tile two weeks later from a new dye lot. It will be close. Close is worse than wrong on a floor, because your eye finds the line every single time you walk in.
Trusting the nominal size on the shelf tag. Tile labeled 12x12 is routinely 11-7/8 inches, so "48 tiles for 48 square feet" is already wrong before you start. The coverage printed on the box is the truth.
Forgetting the backsplash when tiling the kitchen floor. It's a separate surface with its own cuts — count it as its own job or it'll eat your spare tiles.
Ignoring grout joint width in the layout. A 1/8-inch joint across ten tiles eats 1-1/4 inches of your plan, which is how you end up with a 3/4-inch sliver at the far wall.

Factors that affect accuracy

Tile size. Big tiles mean fewer grout lines and faster coverage, but every offcut is a big expensive triangle — small rooms waste large-format tile badly.
Layout pattern. Straight grid is the stingiest with material; diagonal, herringbone, and Versailles patterns turn 10% waste into 15–20%.
Obstacles. Every toilet flange, floor vent, pipe, and doorway notch is a tile sacrificed to the wet saw. Bathrooms waste more than empty rectangles.
Room shape. An L-shaped room forces cuts along two extra edges compared to a simple rectangle of the same square footage.
Tile material. Porcelain cuts clean; cheap ceramic chips and cracks in the cutter, so budget extra. Natural stone varies tile to tile — you cull the ugly ones, which is waste by another name.
Who's setting it. A pro breaks maybe one tile a day. First-time DIYers should add 5% on top of the standard allowance and consider it tuition.

Please note: material estimates are approximate. Always confirm product coverage with the manufacturer and buy a little extra for cuts, waste and future repairs.

Frequently asked questions

How many 12x12 tiles do I need for 100 square feet?

One hundred before waste, since each tile covers exactly one square foot. Add the standard 10% waste allowance — 100 × 1.10 = 110 — and order 110 tiles. For a diagonal layout use 15% instead, which comes to 115.

What waste percentage should I use for tile?

Use 10% for a straight grid layout in a simple room — that's the industry standard. Go to 15% for diagonal patterns, herringbone, or rooms with lots of obstacles like toilets and vents. If this is your first tiling job, add another 5% on top; beginners break more tile, and that's normal.

Can I return extra tiles to Home Depot or Lowe's?

Usually yes, if the boxes are unopened — both stores typically allow returns within 90 days with a receipt. That's exactly why the calculator rounds up to full tiles and you order full boxes: loose spare tiles have no return value, but unopened boxes do. Keep one box of spares from the same lot even so.

Do grout lines change how many tiles I need?

For ordering, no — the calculator ignores grout joints, which keeps the estimate slightly conservative, and that's the safe direction. But joints matter for layout: a 1/8-inch gap repeated across a room shifts where your edge cuts land, so dry-lay a row with spacers before you commit.

Can I use floor tile on the wall?

Generally yes — floor tile is thicker and heavier, so check that your wall and thinset can hold it, and large heavy tiles may need a ledger board while the mortar cures. The reverse is the dangerous one: wall tile on a floor will crack underfoot and gets slippery when wet. Never do that.

What happens if my tile is discontinued mid-project?

This is why attic stock exists. Keep at least one full box from your original dye lot — if a tile cracks in five years and the line is discontinued, that box is the difference between a ten-minute repair and retiling the room. When buying, ask the store whether the line is being phased out.

Should I count the area under cabinets and appliances?

For floor you'll never see, many pros tile under dishwashers and ranges but not under permanent cabinets — it saves material and the cabinet hides the edge. Just be consistent: the calculator counts whatever rectangle you measure, so measure the rectangle you actually intend to tile.