Short answer: a 12′ × 14′ bathroom floor needs about 185 sq ft of tile (168 sq ft net coverage plus 10% waste). In 12" × 24" tiles, that's roughly 93 tiles or 12 boxes. In 12" × 12" tiles, it's 185 tiles or 11 boxes. Diagonal layout adds 5%, mosaic or pattern layouts add 10–15% more. Below is the math, the waste-factor rules every tile setter uses, and the boxes-vs-square-feet conversion that catches DIYers every time.

The formula

Coverage      = Length × Width  (in feet)
Tile order    = Coverage × (1 + waste %)
Tiles needed  = Tile order / sq ft per tile
Boxes needed  = Tiles / tiles per box   (round UP)

Waste-factor rules

• Straight lay (grid) — 10% waste. The default for square or rectangular rooms.
• Diagonal lay (45°) — 15% waste. Every perimeter cut produces a triangle scrap.
• Herringbone or chevron — 15–20% waste. Each tile becomes two cuts at the wall.
• Mosaic or pattern (multi-size) — 15–20% waste plus a 10% "pattern alignment" reserve.
• Curves, niches, recessed shower benches — add another 5%.
• Match a discontinued tile — add 15–20% extra and store the spares. Dye lots are not forever.

Worked example: 12′ × 14′ bathroom floor

Floor area:    12 × 14 = 168 sq ft

Subtract fixtures (toilet, vanity, tub footprint):
  Toilet (closet flange to base):  ~5 sq ft
  Vanity 60" × 22":                 ~9 sq ft
  Tub 30" × 60":                    ~12.5 sq ft
  Total subtraction:                ~26 sq ft

Net tile area:    168 − 26 = 142 sq ft
                  (some setters tile under the vanity and toilet flange
                   for future-proofing — if so, use full 168.)

For DIY safety, calculate from FULL area:  168 sq ft

Add 10% straight-lay waste:
  168 × 1.10 = 184.8 sq ft  →  call it 185 sq ft to order.

Tile-size conversions

Common bathroom-floor tile sizes and what 185 sq ft becomes:

Tile size     Sq ft / tile    Tiles needed    Box typical    Boxes
12" × 12"     1.0             185              15 sq ft       13
12" × 24"     2.0             93               16 sq ft       12
6"  × 24"     1.0             185              16 sq ft       12
8"  × 8"      0.44            420              10 sq ft       19
2"  × 2" mosaic (sheet)        per sheet        10 sq ft       19

NOTE: Mosaic sheets vary 9–13 per sq ft depending on grout-line size.
      Always count by sq ft of sheet, not tile pieces.

Diagonal layout: same room, more tile

Same 12 × 14 floor, diagonal lay:

Net floor:        168 sq ft
Diagonal waste:   15%
Order:            168 × 1.15 = 193 sq ft

In 12" × 24" tiles:    193 / 2 = 97 tiles  →  13 boxes
In 12" × 12" tiles:    193 / 1 = 193 tiles  →  13 boxes

That's 1 extra box vs straight lay — about $40–80 extra cost.

Walls + floor (typical full bathroom remodel)

Add the wet walls (tub surround, shower stall):

Tub surround (3 walls, 5' × 8' tub):
  Back wall:      5 × 5 = 25 sq ft (5 ft up from tub deck)
  End walls:      2 × (3 × 5) = 30 sq ft
  Total:          55 sq ft × 1.15 (more wall cuts) = 63 sq ft

Shower stall (3' × 5', 7' tall):
  3 walls × 7' tall × avg 4' wide = 84 sq ft × 1.15 = 97 sq ft

12 × 14 floor + tub surround:
  185 + 63 = 248 sq ft total

12 × 14 floor + shower stall:
  185 + 97 = 282 sq ft total

Grout coverage

• 12" × 24" with 1/16" joint — ~1 lb of grout per 10 sq ft. 10 lb bag covers ~100 sq ft.
• 12" × 12" with 1/8" joint — ~2 lb per 10 sq ft. 10 lb bag covers ~50 sq ft.
• Mosaic with 1/16" joint — 3–4 lb per 10 sq ft (lots of joint surface).
• Bathroom (185 sq ft, 12×24, 1/16") — ~1 bag (10 lb) of grout. Buy 2.
• Bathroom (185 sq ft, 12×12, 1/8") — 4 bags. Buy 5.

The tile-setter checklist that catches over/under orders

• Measure twice, sketch on graph paper, not memory.
• Ask if the tile is rectified or non-rectified — non-rectified loses ~3% to size variance.
• Order one full extra box past calculated need. Match dye lot.
• Verify tiles per box on the box, not the website. Box counts vary.
• If setting on a heated floor, tile slightly thicker than 1/4" only — thinner tiles crack on the heating cables.
• Calculate trim (bullnose, listello) separately. They sell by linear foot, not sq ft.

Bullnose, trim, and edges (don't forget)

Bullnose for tub deck and door edges (12 × 14 bath):

Tub deck:           3 sides × 5' avg = 15 LF
Door edge:          1 × 3' = 3 LF
Window sill:        1 × 4' = 4 LF
Total:              22 LF + 10% waste = 25 LF

Most bullnose comes in 12" or 24" pieces, sold individually.
At $4–8 per piece, 25 LF in 12" pieces = $100–200.

The most common bathroom-tile mistakes

• Skipping the waste factor. Buys exactly 168 sq ft, runs short by box 11.
• Buying once and ordering more later. Different dye lot. Visible color band on the floor.
• Forgetting bullnose. Stops project for a week mid-install.
• Confusing rectified (true 12.0" × 24.0") with non-rectified (~11.75" × ~23.75"). Joint widths and layout shift dramatically.
• Tiling under the toilet flange when there's no extension ring on hand. Toilet wobbles for the next 10 years.

Run it on your phone

The BuilderCalc app handles tile takeoff for any room shape with built-in waste factors for straight, diagonal, and pattern layouts — plus grout, thinset, and bullnose estimating. Type the room dimensions, pick the tile size, get boxes-needed in seconds. 100% offline. Free on the App Store and Google Play.

Related

• Schluter Ditra vs cement backer board for tile floors
• How many concrete bags for a 4" 20×15 slab
• Drywall sheets for a 12×14 room with 9′ ceiling
• BuilderCalc — construction calculator on iOS + Android

Note: Always check tile box label for actual tiles and square-foot coverage — the "15 sq ft box" can be 14 or 15.4 depending on the manufacturer.