Tile is the project where almost everyone underbuys. The 10% waste factor that works for drywall and paint is way too low for tile, the box quantities don't map to your room size, and certain layouts double your waste before the first cut. Here's how to estimate tile for a bathroom (or anything else) without ending up two boxes short on day three of the install.

The basic formula

Tile is sold in boxes that cover a fixed square footage. The math:

boxes = (area to cover × waste factor) ÷ ft² per box

Always round up. You can't buy 7.3 boxes of tile.

Example: a 5×8 ft bathroom floor (40 ft²) with 12×24 porcelain tile sold in 15.5 ft² boxes, plus 15% waste. 40 × 1.15 = 46 ft². 46 ÷ 15.5 = 2.97 boxes → buy 3 boxes (46.5 ft² total). The tile calculator handles the box- rounding for any tile and room size.

Floor tile math

Floor tile is the simpler case. Measure room length × width, subtract anything not getting tiled (toilet flange? that gets tiled around but counted; vanity footprint? subtract it).

Common bathroom floor sizes and tile needs at 15% waste:

  • 5×8 (40 ft²): 46 ft² of tile
  • 6×10 (60 ft²): 69 ft² of tile
  • 8×10 (80 ft²): 92 ft² of tile
  • 10×12 master bath (120 ft²): 138 ft² of tile

Subtract the vanity if it's a built-in cabinet that won't have tile under it (you can — pros usually do — but some designs skip it for cost reasons).

Wall tile math

Wall tile is where people make the biggest measurement errors. The surfaces you're tiling around a tub/shower:

  • Tub surround: 3 walls × 60" tall × tub width = three rectangles
  • Shower walls: ceiling-height on three or four walls
  • Backsplash behind vanity: 4"–18" depending on style
  • Wainscot or full wall in a powder room

For a standard alcove tub surround (5 ft long, 60" tile height above the tub deck):

  • Long wall above tub: 60 × 60 = 3,600 in² = 25 ft²
  • Two end walls: 30 × 60 each = 25 ft² total
  • Three-wall surround total: 50 ft²
  • Plus 15% waste = 58 ft²

A walk-in shower with full-height tile on three walls (5×3 ft enclosure, 8 ft ceiling) runs around 88 ft² of wall tile. Add the floor and a shower curb if applicable.

Why 15% waste, not 10%

Tile waste runs higher than other materials because:

  • Cuts at every edge. Floors and walls have perimeter cuts that produce unusable scrap. The longer/skinnier the tile, the more waste from cutting to fit.
  • Cuts around obstacles. Toilet flanges, drains, faucet stem-outs, switches. Each one wastes part of a tile.
  • Box variation. Tile is fired in lots — you want at least one extra box from the same lot for repairs over the next decade. Color matching across lots is unreliable.
  • Breakage. Porcelain breaks. Even careful pros lose 2–3% to handling damage.

Use these waste factors:

  • Standard square or subway tile, simple layout: 10–12%
  • Large format (12×24 or bigger): 15%
  • Irregular shapes (hex, fish-scale, picket): 15–20%
  • Diagonal layout (45° rotation): 15–20%
  • Herringbone, basketweave, or chevron pattern: 20–25%
  • Mosaic tile sold by the sheet: 10% (cuts are cleaner)

Standard tile sizes and where each fits

Modern porcelain comes in a huge range. Practical considerations:

  • 2×2 mosaic on mesh: small bathrooms, shower floors (slope to drain), backsplashes. Easy to install, pricier per ft².
  • 3×6 subway: walls and backsplashes. Classic look, low cost ($2–5/ft²), forgiving install. Bad on floors (too small).
  • 6×6 ceramic: the budget bathroom default. Plain, cheap ($1–3/ft²), but small enough that grout lines dominate the look.
  • 12×12: the residential standard. Easy to handle, every store stocks it, $3–8/ft².
  • 12×24: the modern look. Bigger format = fewer grout lines = looks more upscale. $4–10/ft². Requires a flatter substrate (3/16" tolerance).
  • 24×48 large format: high-end residential and commercial. Two-person install, $8–15/ft². Often paired with thinner grout lines for a continuous look.

Calculating boxes vs square feet

Tile boxes don't come in round square footage. Common box sizes:

  • 12×12: usually 11 tiles per box = 11 ft²
  • 12×24: usually 8 tiles per box = 16 ft²
  • 3×6 subway: usually 80 tiles per box = 10 ft²
  • 2×2 mosaic on 12×12 mesh: 1 ft² per sheet, 5 sheets per box = 5 ft²

The actual ft² per box is printed on every box — read it before buying. A “box of tile” can mean anything from 5 to 25 ft².

Pattern impact: when waste doubles

Layout choices have real waste consequences:

Straight stack (grid) or running bond (50% offset):Standard waste factors apply (10–15%).

Diagonal (45° rotation): Add 5–7% to waste. Every perimeter cut is a triangle and the cuts are bigger.

Herringbone:Add 10% to waste. Each tile must be cut to fit a 45° pattern at every wall, and the layout produces dozens of small triangular offcuts that mostly can't be reused.

Penny round, hex, fish-scale: Sold by the sheet but sheets must be cut to fit edges. 15–20% waste typical.

What tile actually costs in 2026

Materials per square foot, contractor-grade not specialty:

  • Builder-grade ceramic 12×12: $1.50–3.00
  • Mid-range porcelain 12×24: $4–8
  • Premium porcelain (large format, wood-look planks): $7–15
  • Natural stone (marble, travertine): $10–25
  • Glass mosaic backsplash sheets: $15–35

Plus consumables: thinset mortar ($30/50-lb bag covers ~75 ft²), grout ($25/25-lb bag), grout sealer ($15), spacers, leveling clips, and a wet saw rental ($60/day) if you don't own one. Budget $150–250 in supplies for a typical bathroom on top of the tile.

Common mistakes to avoid

  • Buying tile from two different lots. Color won't match exactly. Always buy enough from the same lot to finish + leave 5% as attic spare.
  • Ignoring the box quantity. Buying “exactly 50 ft²” means three boxes if the tile is 16 ft² each — that's 48 ft², not 50. Round to whole boxes.
  • Skipping the schluter / edge profile. Where tile meets non-tile (carpet, drywall, tub edge), you need a metal or PVC trim piece for a clean edge. Pros plan this in advance.
  • Underbuying for repairs. Stash one extra box in the attic. Tile lots are discontinued constantly — five years from now when one cracks, you'll be glad you have a match.
  • Calculating wall tile by floor footprint. Wall tile is wall area, not floor area. Measure each wall surface separately.

Quick FAQ

How much tile do I need for a 5x8 bathroom? About 46 ft² for the floor (with 15% waste). For a tub surround, add another 58 ft² of wall tile.

How long does it take to tile a bathroom? A pro tiler does a typical bathroom floor in one day, walls in two, plus a day for grouting after the thinset cures. DIY: triple all of those.

Should I tile under the vanity? Pros tile the whole floor and set the vanity on top. It costs more in tile but means you can swap the vanity later without retiling. Builder-grade jobs skip under the vanity to save material.

Do I need backer board under tile? Yes for floors (cement board or uncoupling membrane like Schluter Ditra) and yes for wet walls (cement board, never green drywall in a shower). Standard drywall is acceptable behind a backsplash.

Run the numbers: the tile calculator gives box count for any tile size and room dimensions, with a configurable waste factor for layouts and patterns.