How to calculate how much tile you need
Tile is sold by the box, but the math starts with square feet. Measure each surface, multiply length by width (or width by tiled height on walls), and add the pieces together. Subtract large openings — a window, a door, a tub or a built-in vanity — but not outlets or switches; you cut around those and the offcuts are waste anyway.
Next, work out how much floor one tile really covers. Tile sizes are nominal: a "12×24" porcelain tile from Floor & Decor measures 11.70 × 23.50 in, and a Daltile "12×12" is 11.81 in. Add the grout joint to each side, multiply, and divide by 144. Divide your area by that figure, add the waste allowance, and round up to whole boxes.
Worked example — a 5 × 8 ft bathroom floor in 12×24 tile: 5 × 8 = 40 sq ft. One tile with a 1/8 in joint covers (23.5 + 0.125) × (11.7 + 0.125) ÷ 144 = 1.94 sq ft, so the floor needs 20.6 tiles. With the 15% recommended for 24-in tile that is 24 tiles. At 7 pieces per box you buy 4 boxes.
Tiles per square foot by size
| Tile | Actual size | Tiles per sq ft | Pieces per box |
|---|---|---|---|
| 3×6 subway | 6 × 3 in | 7.52 | 80 |
| 4×12 subway | 11.81 × 3.94 in | 2.97 | 15 |
| 4×4 4¼ wall | 4.25 × 4.25 in | 7.74 | 100 |
| 6×24 plank | 23.37 × 5.75 in | 1.04 | 11 |
| 12×12 ceramic | 11.81 × 11.81 in | 1.01 | 17 |
| 12×24 porcelain | 23.5 × 11.7 in | 0.52 | 7 |
| 24×24 porcelain | 23.62 × 23.62 in | 0.26 | 4 |
| 24×48 large format | 47.08 × 23.5 in | 0.13 | 3 |
Tiles per square foot include the joint the maker suggests. Carton counts vary by brand — the same 12×24 comes 7 or 8 to a box — so enter yours under "Custom" if it differs.
How much extra tile to buy
MSI recommends 10–15% depending on the pattern, and herringbone runs 15–20%. This calculator uses 10% for a straight grid, 12% for brick offsets, 15% for diagonal and 20% for herringbone. Tile with a 24-in side gets at least 15% because a single bad cut wastes a lot of tile, and rooms under 40 sq ft get another 5% because nearly every piece is a cut. Separately, Daltile suggests keeping about 10% as attic stock: dye lots change, and a cracked tile years from now will not match a new box.
Setting materials that go with the tile
- Thinset: the trowel decides the amount. A 50-lb bag of VersaBond covers 85–95 sq ft with a 1/4 × 1/4 in notch but only 42–47 sq ft with a 1/2 in notch. Tile over 15 in also needs back-buttering. Run the numbers in the thinset calculator.
- Grout: joint width, tile size and thickness all matter. A 3×6 subway tile uses about four times the grout per sq ft of a 12×24. Use the grout calculator to compare brands and bag sizes.
- Backer board: 1/4 in cement board set in thinset for floors over wood, 1/2 in board on walls. The backer board calculator counts sheets, screws and tape.
- Waterproofing: showers need a membrane. RedGard covers 55 sq ft per gallon as a two-coat waterproofing layer — not the 100 sq ft often quoted, which is its crack-prevention rate.
What tile costs to install
homewyse (May 2026) puts installed tile floors at $16.38–$20.21 per sq ft, wall tile at $11.48–$21.27 and backsplashes at $28.31–$49.78, since small jobs carry minimums. Fixr lists porcelain shower walls at $17–$46, with diagonal and herringbone layouts adding about 20% and brick offsets 10–15%.
Common mistakes
- Using the nominal size. A box labeled 12×24 does not cover 2 sq ft per tile.
- Buying exactly the room area. You will run short on cuts and have nothing left for repairs.
- Laying long tile in a ½ offset. ANSI A108.02 limits offsets to 33% on tile longer than 18 in because of warpage.
- Mixing boxes from different lots. Open several boxes and blend them as you lay.
Laying a floating floor instead? Try the flooring calculator. Painting the rest of the room? The paint calculator handles walls and ceilings.