How to Measure for Tile: Floors, Walls, Backsplashes and Showers
Published November 3, 2026 · By Ahmad Parvez
Tile is sold by coverage, but rooms are measured in tape-measure numbers. This guide bridges the two: how to measure each kind of surface honestly, how many tiles live in a square foot for every common size, and how much extra to order so the job never stalls one tile short.
The basic maths (works for every surface)
- Area: length × width, both in feet (convert inches by dividing by 12 — 18 inches is 1.5 ft).
- Odd shapes: split the room into rectangles, work out each one, and add them. An L-shaped kitchen is two rectangles, not a puzzle.
- Tiles needed: total area ÷ area of one tile. A 12×24 tile covers 2 sq ft, so a 100 sq ft floor needs 50.
- Waste: add 10% for straight-set layouts, 15% for diagonal, herringbone or large-format tile, then round up to whole boxes.
That is all the tile calculator does — it just never forgets the waste or the rounding.
Tiles per square foot, by tile size
| Tile size | Tiles per sq ft | Tile size | Tiles per sq ft |
|---|---|---|---|
| 3 × 6 in (subway) | 8 | 12 × 12 in | 1 |
| 4 × 4 in | 9 | 12 × 24 in | 0.5 |
| 6 × 6 in | 4 | 18 × 18 in | 0.44 |
| 3 × 12 in | 4 | 24 × 24 in | 0.25 |
| 8 × 8 in | 2.25 | 12 × 12 in mosaic sheet | 1 sheet |
Worked example: how many 12×12 tiles for 100 sq ft? Exactly 100 tiles before waste; with 10% waste, 110 — and if your box holds 10 tiles, that is 11 boxes. For 120 sq ft, 132 tiles; for 40 sq ft, 44; for 30 sq ft, 33.
How to measure a floor
Measure the longest length and the widest width, skirting boards included — tile runs under them visually even if it stops at the wall. For alcoves and L-shapes, box off each rectangle separately. Do not subtract for fixed units like kitchen islands unless they are truly permanent and will never move; tiling under them costs little and saves a future mismatch. Doorways: add the threshold strip into the main area rather than measuring it separately.
How to measure a kitchen backsplash
A backsplash is a long, low rectangle: the run of countertop multiplied by the height from counter to the underside of the wall cabinets — 18 inches (1.5 ft) is the standard. A 12 ft run is 12 × 1.5 = 18 sq ft. Add the area behind the range if the tile continues up to the hood, and around the window over the sink if you plan to wrap it. Most kitchens land between 15 and 30 sq ft; the average is about 25. Subway tile at 8 tiles per sq ft means a 25 sq ft backsplash needs 200 tiles plus waste.
How to measure a shower or tub surround
Measure each wall separately: width × height up to where the tile will stop (usually 7–8 ft, or the ceiling).
- Standard 3 × 5 shower: back wall 5 ft × 8 ft = 40 sq ft; two side walls 3 ft × 8 ft = 24 sq ft each. Walls total 88 sq ft; floor 3 × 5 = 15 sq ft. About 103 sq ft all-in.
- Tub surround: back wall 5 ft × 7 ft = 35 sq ft; two ends 2.5 ft × 7 ft = 17.5 sq ft each. About 70 sq ft — the figure behind most "standard tub surround" estimates.
- Subtract a large window or a full-height niche only if it is genuinely big; small niches cost more in cuts than they save in tile.
- Shower floors usually take small mosaic (better grip, follows the slope to the drain) — count them as their own line, by the sheet.
Boxes, waste and the cuts nobody plans for
Tiles ship in boxes with a stated coverage — commonly 10 sq ft for a box of ten 12×12s, or 16 sq ft for eight 12×24s — but it varies by maker, so always divide by the coverage printed on your box. Keep one full box unopened if you can: a cracked tile in five years is a five-minute fix if the dye lot is sitting in your garage, and a research project if it is not. Grout joints (typically 1/8–3/16 in) change the count by a percent or two — the waste allowance absorbs them, so measure tile-to-tile and do not subtract joint widths.
Frequently asked questions
How many tiles do I need for 100 square feet?
Divide 100 by one tile's coverage, then add 10% waste. For 12×12 tiles (1 sq ft each) that is 110 tiles. For 12×24 tiles (2 sq ft each) it is 55. For 6×6 tiles (0.25 sq ft each) it is 440. Then round up to full boxes.
How much tile do I need for a shower?
Measure each wall (width × height) and the floor separately, then add them. A standard 3 × 5 ft shower with 8 ft tiling height needs about 88 sq ft for the walls and 15 sq ft for the floor — roughly 103 sq ft before waste. A tub surround is about 70 sq ft.
How do I calculate square footage for a backsplash?
Multiply the length of the countertop run by the height from counter to cabinets — 18 inches (1.5 ft) is standard. A 10 ft run gives 15 sq ft. Add extra for tile continuing behind the range up to the hood or wrapping a window.
How much extra tile should I buy for waste?
Add 10% for straight layouts in rectangular rooms, 15% for diagonal or herringbone layouts, large-format tiles, or rooms with many corners and cuts. The allowance covers cuts, breakages and the occasional dud tile — and leaves spares for future repairs.
How many tiles are in a box?
It depends on the tile: a box of 12×12 tiles commonly holds 10 tiles (10 sq ft of coverage), and a box of 12×24 tiles commonly holds 8 (16 sq ft). Always order by the coverage printed on the box rather than the tile count, and round up to the next whole box.
Do grout lines change how many tiles I need?
Hardly — typical joints of 1/8 to 3/16 of an inch shift the count by a percent or two, and the standard 10% waste allowance absorbs the difference. Measure your walls tile-to-tile without subtracting joint widths.
From measurements to an order list
Feed your numbers into the calculator for tiles, boxes and cost — and the grout guide's companion tool is linked from its page.