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Home & ConstructionTile is one of the least forgiving materials to under-order: dye lots vary between batches, and a discontinued line means a half-tiled bathroom. Over-order wildly, though, and expensive tile sits in your garage forever. The middle path is simple arithmetic plus the right waste allowance.
Here's how pros estimate tile for any floor or wall — and how to adjust for patterns that eat extra material.
Try it yourself: Enter your area and tile size for an exact box count. Tile Calculator →
Tiles per square foot
For square or rectangular tile, the number of tiles covering one square foot is:
Tiles per sq ft = 144 ÷ (length × width in inches)
| Tile size | Tiles per sq ft |
|---|---|
| 12 × 12 in | 1 |
| 6 × 6 in | 4 |
| 4 × 4 in | 9 |
| 12 × 24 in | 0.5 |
So a 120 sq ft bathroom in 12×12 tile needs 120 tiles before waste. (Irregular shapes like hexagons don't follow this — use the manufacturer's coverage per box instead.)
The waste rule: 10% or 15%
Cuts, breakage, and mis-cuts consume tile — there's no way around it:
- 10% waste — straight grid pattern in a simple rectangular room.
- 15% waste — diagonal layouts, herringbone, rooms with lots of corners, or inexperienced installers (no shame — plan for it).
Buy the waste tiles in the same dye lot as the main order. Matching lots later is unreliable, and those spare boxes are also your future repair stock.
Worked example
120 sq ft floor, 12×12 tiles, straight pattern: 120 tiles + 10% = 132 tiles. If tiles come 10 per box, that's 13.2 boxes → buy 14 boxes. Always round boxes up — you can't buy 0.2 of a box.
Walls work the same way
Measure each wall's width × height, subtract large openings (windows, shower niches you won't tile), and apply the same formula. Shower walls and backsplashes usually use smaller tile, so recheck the tiles-per-square-foot for the actual tile size — don't reuse the floor tile's number.
Backsplash math
Backsplashes are small but fiddly: measure the total length × height (a typical 10-ft run at 18 inches tall = 15 sq ft), then apply the same tiles-per-square-foot formula. Because nearly every tile needs cutting around outlets and cabinets, use the 15% waste figure even for straight layouts. For a 15 sq ft backsplash in 3×6 subway tile (8 tiles/sq ft): 120 tiles + 15% = 138 tiles.
Large-format tiles: special rules
Tiles 15 inches or larger need a flatter substrate and are harder to cut without breakage — bump waste to 15% even for simple rooms, and confirm your floor is level within 1/8 inch over 10 feet (large tiles telegraph every bump). Fewer grout lines means a faster install, but each broken tile costs more, so the waste allowance matters doubly.
Ordering checklist
- Measure twice — length × width for floors, each wall separately for walls.
- Convert to tile count with 144 ÷ (L × W), or use box coverage for odd shapes.
- Add 10% waste (simple) or 15% (diagonal, herringbone, heavy cuts, large format).
- Round boxes up — partial boxes don't exist.
- Order everything in one dye lot; keep 1–2 spare boxes for future repairs.
- Don't forget grout, spacers, and sealer — they're separate purchases.
Grout, spacers, and the finishing math
Tile isn't the only quantity: grout coverage is roughly 50–100 sq ft per 10-lb bag depending on tile size and joint width (smaller tiles = more joints = more grout). Spacers are cheap — buy a bag of 100 and don't ration them; consistent joints are what make a floor look professional. And if your tile needs sealing (natural stone, unglazed porcelain), one gallon of sealer covers ~150–200 sq ft per coat.
Frequently asked questions
10% for simple straight layouts, 15% for diagonal patterns, herringbone, or rooms with many corners and cuts. The extras cover breakage during installation and give you matching spares for future repairs.
Tile dye lots vary between production runs, so a later batch may not match in color. Lines also get discontinued. Ordering everything — including waste allowance — in one lot avoids a mismatched floor.
Yes. Every tile meeting a wall at an angle needs a cut, and cuts waste the offcut piece. Diagonal and herringbone layouts typically need 15% waste instead of 10%.
Barely. Standard grout joints (1/8–1/4 in) consume a tiny fraction of coverage. The waste allowance already dwarfs the grout effect — don't adjust for it.
Disclaimer: Irregular tile shapes, mosaics, and manufacturer-specific sizing don't follow the square-tile formula — use the coverage printed on the box for those.