Everyday Life · Practical Life · Home & DIY
Tile Calculator
Calculates the number of tiles needed to cover a rectangular floor or wall area, accounting for tile size and a waste percentage.
Calculator
Formula
N is the total number of tiles to purchase (rounded up to the nearest whole tile). A_room is the total area of the room or surface (length × width). A_tile is the area of a single tile (tile length × tile width). W is the waste percentage (%) added to account for cuts, breakages and offcuts — typically 10% for straight-lay patterns and 15–20% for diagonal patterns.
Source: Standard tiling estimation practice as described in BS 5385 (Wall and Floor Tiling) and general trade guidance from the Tile Association (TTA).
How it works
Tiling any surface is fundamentally an area problem. You need to cover a certain number of square metres, and each tile covers a fixed area determined by its dimensions. The core calculation divides the total room area by the area of one tile to find the minimum number needed. However, tiling is never perfectly efficient — every job produces offcuts along walls, corners and obstacles, and tiles occasionally crack during cutting or installation.
The formula used here is: N = ⌈ (A_room / A_tile) × (1 + W/100) ⌉. The room area (A_room) is simply length multiplied by width in square metres. The tile area (A_tile) is the tile's length multiplied by its width, converted from centimetres to metres. The waste factor W (entered as a percentage) inflates the raw tile count to ensure you have enough material. The ceiling function ⌈ ⌉ rounds the result up to the nearest whole tile, since you cannot buy a fraction of a tile. A waste allowance of 10% is standard for a simple straight-lay grid pattern, while diagonal or herringbone layouts — which require more cuts — typically warrant 15–20%.
In practical terms, it's always better to over-order slightly than to under-order. Tile batches (known as dye lots) can vary slightly in colour and texture between production runs. If you run short and need to reorder, the new tiles may not match your existing ones perfectly. Most suppliers will accept returns on unopened boxes, so buying one box extra is low risk and can save significant hassle.
Worked example
Suppose you are tiling a bathroom floor that measures 2.8 m × 2.2 m, using square tiles that are 45 cm × 45 cm, with a waste allowance of 10%.
Step 1 — Calculate the room area:
A_room = 2.8 × 2.2 = 6.16 m²
Step 2 — Calculate the area of one tile:
A_tile = (45 ÷ 100) × (45 ÷ 100) = 0.45 × 0.45 = 0.2025 m²
Step 3 — Calculate the exact number of tiles needed (no waste):
Tiles = 6.16 ÷ 0.2025 = 30.42 tiles
Step 4 — Apply the waste allowance:
Tiles with waste = 30.42 × (1 + 10/100) = 30.42 × 1.10 = 33.46 tiles
Step 5 — Round up to whole tiles:
⌈33.46⌉ = 34 tiles
You should purchase 34 tiles for this bathroom floor. If tiles come in boxes of 6, you would need to buy 6 boxes (36 tiles), keeping 2 spare for future repairs.
Limitations & notes
This calculator assumes a simple rectangular room with no cutouts for islands, fireplaces, bathtubs or other fixed features. For rooms with irregular shapes, break the area into smaller rectangles, calculate each separately, and sum the tile counts. The calculator also does not account for grout joint width — for very large tiles or wide grout lines, the effective number of tiles per square metre changes marginally. The waste percentage is a general guideline; your actual waste will depend on tile size relative to room dimensions, the complexity of the pattern, the skill of the installer, and the number of obstacles. Always consult your tiler for a precise quote on complex projects. This tool is intended for planning and budgeting purposes, not as a substitute for professional measurement and estimation.
Frequently asked questions
What waste percentage should I use for a standard tile layout?
For a simple straight grid pattern aligned with the walls, 10% is the industry standard waste allowance. For diagonal (45°) patterns or complex herringbone layouts, use 15–20% because far more cuts are required along the perimeter. If your room has many obstacles such as pillars or alcoves, add an extra 5% on top.
Does tile size affect how much waste I should expect?
Yes. Larger tiles generally produce more waste per cut, but fewer cuts are needed overall. Very small mosaic tiles tend to be more efficient around edges. As a rule, the bigger the tile relative to the room dimensions, the more noticeable off-cuts will be — particularly in narrow corridors or small bathrooms where nearly every tile along the edge must be cut.
Should I include areas covered by furniture or appliances?
Yes, you should tile under furniture and appliances unless they are permanently built-in (like a fitted bath panel that is tiled before installation). Tiles under movable furniture protect the subfloor and allow for future rearrangement. It also makes calculating area much simpler to use the full room dimensions rather than trying to subtract furniture footprints.
How do I calculate tiles needed for a wall as well as a floor?
Run the calculator separately for each surface (floor, then each wall you plan to tile). For walls, treat height as 'length' and width as 'width'. Don't forget to subtract the area of windows, doors and mirrors where tiles will not be laid. Sum the tile counts from each calculation and add a single waste allowance at the end, or apply the waste percentage to each surface individually.
What does 'dye lot' mean and why does it matter when buying tiles?
A dye lot (or batch number) refers to a specific production run of tiles. Even identical tile models can show subtle differences in shade, texture or size between batches due to variations in raw materials and kiln temperatures. If you run short of tiles mid-project and reorder, the new batch may not match your existing tiles closely enough to be invisible. Always buy all your tiles from the same batch if possible, and keep a few spares in case a tile chips or cracks in the future.
Last updated: 2025-01-15 · Formula verified against primary sources.