Tile is unforgiving to under-order. Unlike paint, you cannot blend a fresh batch into a half-finished floor — a new dye lot may be a shade off, and a discontinued line may be gone entirely. That makes the tile count one of the most important numbers in any bathroom, kitchen or floor project. This guide shows how the calculator arrives at its figure and how to set the waste factor for your layout.
The tile-counting formula
The principle is simple: divide the area you are covering by the footprint of a single tile, then add a margin for cuts and breakage.
Base tiles = area ÷ effective footprint, rounded up
Tiles to buy = base tiles × (1 + waste factor), rounded up
The grout joint matters because the tile plus its surrounding joint is what actually occupies space on the floor. A 12×12 in tile with a 1/8 in joint behaves like a 12.125 in tile for spacing purposes. On small tiles this difference adds up quickly; on a mosaic sheet it can change the count noticeably.
How to measure the area
For a rectangular floor, multiply length by width. For anything irregular, break the space into rectangles, calculate each, and add them together. A few practical notes:
- Measure the actual tiled area, not the room footprint. Subtract permanent fixtures like a kitchen island or a built-in vanity that won't be tiled under.
- Tile under appliances anyway in kitchens and laundry rooms — it gives a level surface and lets you replace appliances later without a gap.
- For walls and backsplashes, measure height × width of the tiled zone. A backsplash is usually the run of countertop multiplied by the gap up to the cabinets (often 16–18 in).
Choosing the right waste factor
The waste factor is the part people guess wrong. It exists because tiles at the edges of the room must be cut, and the off-cuts are rarely reusable. The more cuts a layout demands, the more waste it produces.
| Layout | Waste factor | Why |
|---|---|---|
| Straight / grid | 10% | Cuts only at walls |
| Diagonal (45°) | 15% | Every edge tile is a triangular cut |
| Herringbone / chevron | 15–20% | Many angled cuts throughout |
| Large-format (24 in+) | 15% | Big off-cuts can't be reused |
| Small rooms with many corners | 15%+ | More edges relative to area |
A larger, simpler room can sit at the lower end; a small, complex bathroom should use the higher end. When in doubt, round up — leftover full tiles are returnable at most stores, while a shortfall costs you a second trip and a possible dye-lot mismatch.
A worked example
Say you are tiling a 10 × 8 ft floor (80 sq ft) with 12×12 in porcelain, 1/8 in joints, in a straight layout:
- Effective tile footprint = (12 + 0.125) × (12 + 0.125) ≈ 147 sq in = 1.02 sq ft
- Base tiles = 80 ÷ 1.02 ≈ 79 tiles
- With 10% waste = 79 × 1.10 ≈ 87 → buy 87 tiles
- At 10 tiles per box that's 9 boxes (90 tiles), giving a small spare stock.
Don't forget the grout and adhesive
Tile is only one line on the shopping list. You will also need thin-set mortar or adhesive (coverage depends on tile size and trowel notch) and grout (more for wider joints and smaller tiles). As a rough planning figure, a 50 lb bag of thin-set covers roughly 40–60 sq ft with a standard trowel, and grout needs scale with joint width. Use unsanded grout for joints under 1/8 in and sanded grout for wider joints.
Once your tile count is set, the related calculators below help you finish the shopping list — grout quantity, adhesive coverage and the underlying square footage.
Frequently asked questions
How many tiles do I need per square foot?
It depends on tile size. A 12×12 in tile is exactly 1 tile per square foot. A 6×6 in tile is 4 per square foot; an 18×18 in tile is about 0.44 per square foot. The calculator works this out from the exact tile dimensions you enter, including the grout joint.
How much extra tile should I buy for waste?
Add 10% for a straight layout, 15% for diagonal, and up to 20% for herringbone or other complex patterns. Larger rooms and intricate cuts waste more. Always round up to full boxes and keep a few spares for future repairs.
Does grout joint width change how many tiles I need?
Yes, slightly. Wider grout joints mean each tile effectively covers a little more area, so you need marginally fewer tiles. Our calculator adds the joint width to each tile dimension to reflect this.
How do I calculate tiles for a wall instead of a floor?
Exactly the same way — enter the wall height and width as the area dimensions. For backsplashes, measure the height from countertop to the underside of the cabinets.
Should I buy tile by the box or individually?
Tile is sold by the box, and boxes from different production runs can vary slightly in shade (the “dye lot”). Buy all your tile, plus the waste allowance, in one purchase from the same lot.