About the Tile Calculator
This tile calculator tells you how many tiles to buy for a floor, shower wall or kitchen backsplash. Enter the length and width of the area in feet, the tile dimensions in inches and the grout joint width, and it works out how many square feet each tile really covers, how many tiles fill the space and how many boxes to order.
It is designed for homeowners pricing a bathroom remodel, DIY tilers planning a backsplash and contractors double-checking a take-off. The waste allowance covers cuts at walls, breakage and a few spares for future repairs: 10% suits a simple square room with a straight lay, while 15–20% is safer for diagonal or herringbone patterns, small rooms with many cuts, or large-format tile.
For L-shaped rooms, split the floor into rectangles and run the calculator for each, or enter the combined square footage as a single rectangle (for example 150 × 1). Always round up to whole boxes and buy from the same dye lot so the color matches.
With the default inputs, the tiles needed (incl. waste) is 130. Change any value above to recalculate instantly.
How to use the tile calculator
- 1Measure the length and width of the floor or wall area in feet.
- 2Enter the tile size in inches and the grout joint you plan to use.
- 3Choose a waste allowance — 10% for straight lays, 15–20% for diagonal patterns.
- 4Enter the tiles per box and box price from the product listing.
- 5Order the number of boxes shown, all from the same dye lot.
Formula and method
Each tile effectively covers its own face plus one grout joint in each direction, so the coverage per tile is (tile length + joint) × (tile width + joint) in square inches, divided by 144 to convert to square feet. Dividing the area (length × width in feet) by that coverage gives the exact number of tiles for a perfect, cut-free layout.
Real installations lose tiles to edge cuts, breakage and pattern offsets, so the waste percentage is added before rounding up to whole tiles. The box count is then rounded up again because tile is sold by the carton. Cost is boxes × price per box, and cost per square foot divides that by the tiled area.
- L, W
- Length and width of the area (ft)
- a, b
- Tile length and width (in)
- g
- Grout joint width (in)
- waste%
- Allowance for cuts and breakage
Worked examples
12 × 10 ft bathroom floor with 12×12 tile
With a 1/8-inch joint each 12-inch tile covers 12.125² ÷ 144 = 1.021 sq ft, so 120 sq ft needs 117.5 tiles. Adding 10% waste gives 130 tiles, which is 13 boxes of 10 at $30 — $390, or $3.25 per sq ft.
Subway tile backsplash
An 8 ft by 18 in backsplash is 12 sq ft. Each 3×6 subway tile with a 1/16-inch joint covers 0.129 sq ft, so the wall takes 93 tiles; 15% waste for the many cuts around outlets brings it to 108 tiles, or 3 boxes of 40.
Large-format 24×24 porcelain in a living room
A 300 sq ft room covered with 24-inch tiles and a 3/16-inch joint needs 73.8 tiles before waste and 82 with 10% extra. At 3 tiles per box that is 28 boxes, costing $1,680 or $5.60 per sq ft.
Frequently asked questions
How many tiles do I need for 100 square feet?+
With 12×12 tiles and a 1/8-inch grout joint you need about 98 tiles for 100 sq ft, or 108 with 10% waste. Smaller tiles need many more: 6×6 tiles take roughly 385 before waste.
How much extra tile should I buy?+
Buy about 10% extra for a simple straight layout and 15–20% for diagonal, herringbone or large-format tile, or rooms with lots of corners. Keep a few spare tiles for future repairs because dye lots change.
Does grout width change how many tiles I need?+
Yes, slightly. Wider joints mean each tile covers a bit more area, so you need fewer tiles. The effect is small for big tiles but noticeable for mosaics and small subway tile.
How do I calculate tile for a wall?+
Measure the wall width and the height you plan to tile, multiply them for square footage, then subtract windows or doors larger than a few square feet. Enter the result as length × 1 if you already know the total area.
How many square feet are in a box of tile?+
It varies by product: boxes of 12×12 tile usually hold 10–15 sq ft, while large 24×24 porcelain boxes often cover 12–16 sq ft (3–4 tiles). Check the carton label and enter tiles per box.