Tiling a bathroom is one of those jobs where running out of material halfway through is a real problem. Tiles come in batches (sometimes called lots or shade runs), and a box bought a month later may not match the colour of the first. Working out the area properly before you order, and adding the right allowance for cuts and breakages, means you can buy everything from one batch.
Floors
Most bathroom floors are close to rectangular, but few are perfectly so. Measure:
- The main length and width, wall to wall.
- Any recess, such as a space beside the bath or a doorway alcove.
- Obstacles you won't tile under, like a fitted vanity unit or bath. Some people tile under a freestanding bath and others don't; decide before measuring.
Multiply length by width for each rectangle and add them together. Subtract areas that won't be tiled.
Example: a floor 8 ft × 6 ft with a built-in bath 5 ft × 2.5 ft that won't be tiled underneath.
- Total: 8 × 6 = 48 sq ft
- Bath: 5 × 2.5 = 12.5 sq ft
- Tiled floor: 48 − 12.5 = 35.5 sq ft
Walls
Walls are measured wall by wall. For each one, multiply the width by the height you're tiling to, then subtract windows and doors.
- Full height: floor to ceiling.
- Half height: often to around 4 ft, or to a dado line.
- Splashback: a strip behind a basin, often two or three tile rows high.
Example: a wall 8 ft wide tiled to 4 ft, with a 2 ft × 2 ft window in the tiled area.
- Wall: 8 × 4 = 32 sq ft
- Window: 2 × 2 = 4 sq ft
- Tiled area: 32 − 4 = 28 sq ft
Remember to include window reveals (the sides and sill inside the window opening), which are easy to forget and use a surprising number of cut tiles.
Shower surrounds
A walk-in shower or bath-shower usually has three tiled walls. Measure each from the top of the tray or bath to your chosen height (commonly 6.5 to 7 ft for showers). Add niches and shelves: a recessed niche has a back, two sides, a top and a bottom to tile.
Example: an alcove shower with a 3 ft back wall and two 3 ft side walls tiled to 7 ft.
- 3 walls × 3 ft × 7 ft = 63 sq ft
Adding the waste allowance
You always need more tile than the measured area, because tiles get cut at edges, around pipes and at corners, and some break. Typical allowances are:
| Layout | Extra to add | |---|---| | Straight grid, simple room | 10% | | Lots of cuts, small room, many obstacles | 15% | | Diagonal or herringbone layout | 15–20% | | Large-format tiles (easy to break, big offcuts) | 15% or more |
For the floor example with a straight layout: 35.5 × 1.10 ≈ 39.1 sq ft.
Converting area to boxes
Tile boxes list the area they cover, for example 10.76 sq ft (1 m²) per box. Divide your total including waste by the coverage and round up:
39.1 ÷ 10.76 ≈ 3.6, so 4 boxes
Check the batch or shade number on every box before you start, and keep at least one spare tile (ideally a few) for future repairs.
Trims, adhesive and grout
Once you have the area, other quantities follow:
- Adhesive: coverage depends on tile size and trowel notch. Check the product label, which usually gives square feet or square metres per bag.
- Grout: depends on joint width, tile size and thickness. Manufacturers provide coverage charts.
- Edge trims: measure in linear feet along exposed edges and external corners.
Double-check with a calculator
Adding up several walls, subtracting windows and then applying a waste factor is where errors creep in. Running your measurements through the tile tool on SquareFootageCalculator.org is a quick way to confirm the total before you order.
Summary
Measure floors and each wall separately, subtract areas you won't tile, remember window reveals and niches, then add 10–20% depending on layout. Convert to boxes, round up and buy from a single batch. It's the cheapest insurance against mismatched tiles in the middle of the job.