How to use the tile calculator
- Measure the area. For a rectangular floor, measure length and width at the widest points. For an L-shaped room, split it into rectangles, calculate each one, and add the results (or add the areas yourself and choose I know the area). For a wall or backsplash, use the width and height of the tiled section.
- Enter the tile size. Use the actual tile size printed on the box, not the "nominal" name. A "12 × 24" porcelain tile is often 11¾ × 23½ inches.
- Enter the grout joint. 1/16 in (0.0625) for rectified tile, 1/8 in (0.125) for most floor tile, 3/16–1/4 in for handmade or uneven tile.
- Choose a waste allowance. 10% for a straight lay in a simple room, 15% for diagonal or herringbone, and up to 20% for small rooms with many cuts.
- Add tiles per box and a price to see how many boxes to order and what the tile will cost.
The tile formula
Each tile covers its own face plus one grout joint in each direction, so the footprint of a single tile is:
Tile footprint (sq ft) = (tile length + joint) × (tile width + joint) ÷ 144
Then:
Tiles = area ÷ tile footprint × (1 + waste %)
Boxes = tiles ÷ tiles per box, rounded up
Counting the grout joint matters more than people expect with small tile. For a 2 × 2 inch mosaic with a 1/8 inch joint, the joint adds about 13% to each tile's footprint; for a 24 × 24 inch tile it adds about 1%.
Worked example
A kitchen floor measures 12 ft × 10 ft = 120 sq ft. You are laying 12 × 12 inch tile with a 1/8 inch grout joint, straight pattern, 10% waste, sold 10 tiles per box.
- Tile footprint: 12.125 × 12.125 ÷ 144 = 1.021 sq ft
- Tiles without waste: 120 ÷ 1.021 = 117.5 → 118 tiles
- With 10% waste: 117.5 × 1.10 = 129.3 → 130 tiles
- Boxes: 130 ÷ 10 = 13 boxes
At $2.50 per sq ft, the tile itself costs about 120 × 1.10 × $2.50 ≈ $330. Thinset, grout, backer board and trim are extra.
Tips for ordering tile
- Buy everything from one lot. Tile color and even size can vary between production runs. Check that the lot or shade number matches on every box.
- Keep a spare box. If a tile cracks in five years, you will not find the same lot. Most installers recommend keeping at least a few spare tiles after the job.
- Large-format tile needs more waste, not less. Each cut piece of a 24 × 48 inch tile is a large share of a box, and offcuts are rarely reusable.
- Pattern changes the math. Diagonal, herringbone and chevron layouts create cuts along every edge. Use 15–20%.
- Measure walls in sections. Subtract windows, but not small outlets or switches — the tile around them still gets cut and wasted.
Frequently asked questions
How much extra tile should I buy?
Buy about 10% extra for a straight layout in a normal room and 15% for diagonal or herringbone patterns. Small rooms, many corners or large-format tile can justify up to 20%.
Do I include the grout line when calculating tiles?
Yes. Each tile occupies its own size plus one joint width in each direction. Ignoring the joint slightly overestimates tile needs; the effect is small for large tiles and larger for mosaics.
How do I calculate tile for an L-shaped room?
Split the room into two or more rectangles, find the square footage of each, and add them together. Enter the total using the "I know the area" option.
How many square feet are in a box of tile?
It varies by product, typically 8 to 16 sq ft per box for floor tile. The coverage is printed on the box; divide it by the area of one tile to get tiles per box.
Is it cheaper to buy tile by the box or by the piece?
Most stores sell floor tile only by the box. If you can buy individual pieces, use the "per tile" price option to compare.