Stop Guessing at the Tile Store
Running short mid-project is the classic tiling nightmare: the store is out of your dye lot, and the new batch is a shade off. Buying blind in the other direction is just as painful — a stack of expensive leftover boxes you can never return. Both problems come from the same place: not doing the area math before you shop.
This free tile calculator does that math for you. Enter the length and width of your floor or wall, pick your tile size — 12×12, 18×18, 24×24, classic subway, or a custom size — and it returns the exact tile count, a proper waste allowance, how many boxes to buy, and even a grout estimate. It works for floors, walls, backsplashes, and shower surrounds alike.
How this was calculated
Grout is an estimate based on a 1/4 in joint depth (about two-thirds of a 3/8 in tile) and sanded cement grout density. Always confirm with your grout manufacturer’s coverage chart and buy one spare box of tile for future repairs.
How to Use This Calculator
- Measure the area. Measure the length and width of the floor or wall in feet. For a wall, measure the area you actually plan to tile — backsplash height, for example — not the whole wall.
- Pick your tile size. Choose 12×12, 18×18, 24×24, or 3×6 subway from the dropdown, or select “Custom size” and enter the tile’s length and width in inches.
- Set the waste allowance. Keep 10% for a straightforward grid layout. Switch to 15% for diagonal layouts, rooms with lots of corners, or patterns like herringbone that generate more cuts.
- Enter tiles per box. Check the tile box or product page — a 12×12 tile commonly comes 10 to 15 per box. The calculator rounds up to whole boxes.
- Choose your grout line width. Wider joints consume more grout. The calculator turns your joint width into a pounds-of-grout estimate plus 10-lb bag count.
- Calculate and shop with the list. Buy the tile count shown (it already includes waste), the box count, and the grout — plus one spare box of tile for future repairs.
What Is a Tile Calculator?
A tile calculator converts the square footage of your project into a shopping list. The core operation is simple division: total area divided by the area of one tile. But a useful calculator goes further, because real projects have complications the raw division misses.
First, cuts waste tile. Every doorway, corner, and edge forces partial tiles that usually can’t be reused, which is why contractors add 10% for simple layouts and 15% for diagonal ones. Second, tile is sold by the box, so the count has to round up to whole boxes — ordering 8.3 boxes is not an option. Third, the grout matters: joint width and tile size determine how much grout the project drinks, and running out of grout is a special kind of frustration because color matching across batches is unreliable.
This calculator handles all three: the waste factor is built into the headline number, boxes are rounded up automatically, and the grout estimate uses the industry-standard joint-volume formula rather than a guess.
The Formula (With a Worked Example)
Boxes = ⌈tiles ÷ tiles per box⌉
Grout (lb) ≈ area in ft² × (tile L + tile W) ÷ (tile L × tile W) × joint width in in × 2.29
Worked example: a 10 ft × 12 ft bathroom floor with 12×12 in tiles, 1/4 in grout lines, 10% waste, and 12 tiles per box.
- Area = 10 × 12 = 120 ft² = 17,280 in²
- One tile = 12 × 12 = 144 in²
- Exact tiles = 17,280 ÷ 144 = 120
- With 10% waste = 120 × 1.10 = 132 tiles to buy
- Boxes = ⌈132 ÷ 12⌉ = 11 boxes
- Grout ≈ 120 × 24 ÷ 144 × 0.25 × 2.29 ≈ 11.5 lb → 2 × 10-lb bags
Try these exact numbers in the calculator above — you will get 132 tiles, 11 boxes, and about 11.5 lb of grout.
Tips for an Accurate Tile Order
- Measure twice, in feet and inches. A 6-inch error on a 10-foot wall changes the count by 5%. Measure each wall separately — rooms are rarely perfectly square.
- Subtract what you won’t tile — then add it back mentally. For walls with doors or windows, subtract those areas for the base count, but keep the waste percentage at 15%: the extra cuts around openings eat the savings.
- Always buy the spare box. Tile dye lots change, and a cracked tile in three years is a two-day fix if you have a spare, or a re-tiling project if you don’t.
- Go 15% for diagonal and patterned layouts. Herringbone and diagonal installations can waste nearly double the tile of a straight grid — 15% is the minimum, and 20% is safer for complex patterns.
- Check box coverage, not just tile count. Some boxes list square footage rather than tile count. Divide your area by the box coverage and round up, then cross-check against the calculator.
- Buy all grout at once. Grout color varies slightly between batches. One purchase for the whole project keeps the joints uniform.
Layout Patterns Change Your Tile Count
The waste percentage is not really about the room — it is about the pattern. A straight grid reuses most offcuts, but every angled pattern throws away wedge-shaped pieces at every wall. Use these allowances on top of the base tile count:
| Layout pattern | Extra to buy | Why it wastes more |
|---|---|---|
| Straight / grid | 10% | Offcuts from one row usually start the next |
| Offset (brick bond) | 10-15% | Staggered ends create more unusable short pieces |
| Diagonal (45 degrees) | 15% | Every edge tile is cut on an angle; corners rarely reuse |
| Herringbone | 20% | Rectangles meet at 45 and 90 degrees, so border cuts multiply |
Worked example. A 100 sq ft floor in herringbone with 12×24 tiles (2 sq ft each): 100 ÷ 2 = 50 tiles, plus 20% pattern waste = 60 tiles.
More Construction Tools
Frequently Asked Questions
How do I calculate how many tiles I need?
Multiply the length by the width of the area in feet to get square footage, convert to square inches (multiply by 144), and divide by the area of one tile in square inches. Then add 10% for waste — 15% for diagonal layouts — and round up to whole boxes.
How much extra tile should I buy for waste?
Buy 10% extra for a straightforward grid layout and 15% for diagonal layouts, rooms with many corners, or patterns like herringbone. The extra covers cuts, breakage, and one spare box for future repairs.
How many 12×12 tiles do I need for 100 square feet?
One hundred square feet is 14,400 square inches, and a 12×12 tile covers 144 square inches, so you need exactly 100 tiles. With the standard 10% waste allowance, buy 110 tiles.
Can I use this calculator for wall tiles and backsplashes?
Yes. Measure the height and width of the area you plan to tile in feet and enter them as length and width. For walls with windows or doors, subtract those areas from the total — but keep the 15% waste setting, since cuts around openings waste more tile.
How much grout do I need for my tile project?
It depends on tile size and joint width: smaller tiles and wider joints need more grout. As a rough guide, a 10 lb bag covers about 100 square feet of 12×12 tile with 1/4 in joints. The calculator above gives a precise estimate from your exact tile size and joint width.
What tile sizes does the calculator support?
Built-in presets cover 12×12, 18×18, 24×24, and 3×6 subway tile. The custom option accepts any rectangular tile up to 120 inches per side — mosaic sheets, plank tiles, and large-format panels all work.
Why does the calculator round up to whole boxes?
Tile is sold by the box, not by the tile, so any fraction of a box means buying the whole box. Rounding up also adds a small safety margin on top of the waste allowance, which is exactly what you want before the mortar is mixed.
Do I need to account for the grout lines in the tile count?
No — and this is a common misconception. Grout lines are thin (1/8 to 1/4 in) and their effect on the tile count is far smaller than the waste allowance already covers. The 10–15% waste factor absorbs it completely.
How many tiles do I need for a herringbone pattern?
Divide your area by the tile’s coverage, then add 20%. For a 100 sq ft floor with 12×24 tiles (2 sq ft each), that is 50 tiles × 1.20 = 60 tiles. Herringbone wastes more than any common layout because every border tile is cut at an angle.
Does a diagonal layout really need 15% extra tile?
Yes. Laying tiles at 45 degrees to the walls means every tile along all four walls is cut diagonally, and the triangular offcuts almost never match another gap. Pros order 15% extra for diagonal floors — up to 20% in small rooms with many corners, where the cut-to-whole-tile ratio is worst.