Tile counting is one division problem — area divided by tile size — but a real job also needs thinset, grout, backerboard, and trim, each on its own rule. Get the square footage and the right waste factor and the rest follows. This guide runs from tile counts to showers, substrate prep, and cost — distilling the 100 questions tilers and DIYers ask most into one readable pass.
Every tile estimate starts with surface area divided by one tile's footprint. Tiles are sized in inches, rooms in feet, so the reconciling step is dividing a tile's square inches by 144 to get square feet.
For an L-shaped or irregular floor, split it into rectangles, area each, and add. Metric works the same — total m² ÷ one tile's m². If you want to be precise about wide joints, add the joint width to both tile dimensions before multiplying.
The density is fixed per tile size, so pick your tile and multiply by area:
| Tile size | Coverage | Per sq ft |
|---|---|---|
| 4″ × 4″ | 16 sq in | 9 |
| 3″ × 6″ (subway) | 18 sq in | 8 |
| 6″ × 6″ | 36 sq in | 4 |
| 12″ × 12″ | 144 sq in | 1 |
| 12″ × 24″ | 288 sq in | 0.5 (1 tile / 2 sq ft) |
| 18″ × 18″ | 324 sq in | 0.44 (1 / 2.25 sq ft) |
| 24″ × 24″ | 576 sq in | 0.25 (1 / 4 sq ft) |
In practice you buy by the box: divide your total square footage (with waste) by the box's printed coverage and round up to whole boxes.
A 100 sq ft floor in 12×12 tile = 100 tiles; +10% waste = 110 tiles. A 40 sq ft backsplash in 3×6 subway = 40 × 8 = 320; +10% = 352 tiles.
Waste covers tiles broken in cutting, ruined drilling for valves, and slivers trimmed at edges. Pattern is the main driver — anything that forces angled cuts raises it:
| Layout | Waste factor |
|---|---|
| Straight grid / running bond | 10% |
| Diagonal (45°) or herringbone | 15–20% |
| Rounded / radiused walls | 20% |
| Shower niche & intricate accent bands | 25–30% |
Tiles fired in different kiln runs carry different dye-lot numbers, with slight shade and size shifts. Order your full quantity (plus waste, rounded to whole boxes) in one go, or a later top-up may not match.
Thinset mortar bonds tile to the substrate, and its coverage depends entirely on trowel notch — bigger tiles need a deeper notch and burn through more mortar:
| Trowel notch | Coverage | Use |
|---|---|---|
| 1/4″ × 1/4″ square | 80–90 sq ft | Small / mosaic tile |
| 1/4″ × 3/8″ square | 60–70 sq ft | Standard floor tile |
| 1/2″ × 1/2″ square | 40–50 sq ft | Large-format (15″+) |
So a 200 sq ft floor with a 1/4″×3/8″ trowel at ~65 sq ft/bag is 200 ÷ 65 = 3.08 → 4 bags. Cement backerboard (Durock/WonderBoard) gives a flat, moisture-stable bed — a 3×5 sheet covers 15 sq ft, so a 120 sq ft room is 120 ÷ 15 = 8 sheets, +10% = 9. For wet areas, add an uncoupling membrane (Schluter-DITRA, sold in 54 or 150 sq ft rolls, +5% for overlaps) or a liquid waterproofing like RedGard at 40–50 sq ft/gal across two coats.
Grout fills the joints, and its quantity hinges on how many joint lines you have. Small tiles have far more joint per square foot, so they eat dramatically more grout:
| Tile | Grout needed |
|---|---|
| 12″ × 12″ | 6–8 lb |
| 2″ × 2″ mosaic | 25–30 lb |
Epoxy grout covers the same volume as cement grout but must be mixed in exact factory ratios. Budget for a few accessories too: a grout release agent on textured stone (~150–200 sq ft/quart), and grout sealer for the finished lines (~400–600 linear ft/pint).
Vertical work uses simple area shortcuts. A kitchen backsplash is the countertop run × the standard 1.5 ft height between counter and cabinets. A 3-wall tub surround is the three wall lengths added, times the target height above the rim — e.g. (5 + 3 + 3) = 11 linear ft × 6 ft = 66 sq ft.
Trim and detail pieces are counted by linear foot: accent listello strips and pencil liners by perimeter length, and bullnose by the total linear footage of exposed outer edges. A recessed shower niche adds its back wall plus the four return sides — carry a 30% waste factor on it for the small custom cuts. And slope a shower pan ¼″ per foot toward the drain.
A tile job is only as good as what's under it. Several prep layers each get their own takeoff:
Never patch a shower wall with gypsum joint compound — it dissolves when wet; use a polymer-modified cement patch.
A few tile types and trims follow their own rules:
Total cost stacks tile, thinset, grout, backerboard, and trim against local prices, plus delivery and tax.
| Item | Typical figure |
|---|---|
| Ceramic tile (material) | $1.50–$4.00 / sq ft |
| Porcelain tile | $3.00–$10.00+ / sq ft |
| Natural stone | $8.00–$25.00+ / sq ft |
| Floor install labor | $5–$15 / sq ft ($12–$25+ for shower walls) |
| 150 sq ft bath floor | 2–4 days |
Essential DIY rentals are a diamond-blade wet saw for clean porcelain cuts and a mortar mixer drill attachment. A manual snap cutter handles light edge trims.
Two consumables to remember: tile spacers (~4 per tile) for uniform joints, and leveling clips to prevent lippage (~4 per small tile, 6–8 for large/plank). Per TCNA, install flexible expansion joints every 20–25 ft on interior floors (8–12 ft exterior), and fill drain and corner joints with 100% silicone caulk rather than rigid grout — a 10.3 oz tube yields ~25–30 linear ft.
Map the room with a tape, re-run your tile and box counts, and cross-check the supplier invoice before opening any boxes. Snap perpendicular chalk lines through the room center and confirm a true 90° with the 3-4-5 rule so the layout stays square across the whole floor. For cleanup, wipe grout haze with a damp sponge during install; stubborn haze comes off with a mild acidic haze cleaner after curing.