Tile and flooring calculator guide
The calculator above turns a room's dimensions into the one answer every tile shopper actually needs — how many boxes to buy — along with the grout and adhesive to go with them, for one room or a whole job, in metric or imperial, all in your browser.
The guide below explains how to work out tiles from floor area and tile size, why the layout pattern changes how many spare tiles you need, how the grout estimate comes from the joint geometry rather than a vague rule of thumb, and worked examples you can reproduce by hand.
How many tiles do I need?
To work out how many tiles you need, divide the floor area by the area of one tile, then add an allowance for cuts and breakages. Tiles are sold by the box, so the real shopping question is how many boxes that rounds up to.
In short: tiles = floor area ÷ tile area × (1 + waste), then boxes = tiles ÷ tiles-per-box, rounded up. The calculator does every step as you type and rounds up to whole boxes, but the maths is simple enough to check by hand.
As a rule of thumb, a 600 × 600 mm tile covers 0.36 m², so a 4 m × 5 m (20 m²) room needs about 56 tiles before waste and 62 with a 10% allowance — which the calculator turns into the exact boxes to buy and the tiles you'll have spare.
How this calculator works
You describe the job; the calculator handles the arithmetic. Add a room and enter its width and length — always dimensions, never a raw area, so a unit mix-up can't silently double your order. Set the tile size, the layout pattern and how many tiles come in a box, and it returns the floor area, the tiles needed, the boxes to buy and the spare tiles per room and for the whole project.
The layout pattern sets a sensible default waste allowance — more for diagonal and herringbone, less for a straight grid — which you can override. Grout joint width, tile thickness, grout bag size and an optional adhesive estimate live in the assumptions panel, so you can match exactly what you are buying. Switch between metric (m, mm, kg) and imperial (ft, in, lb) at any time and every value converts.
Results can be exported to CSV for a spreadsheet or printed as a clean shopping list. Everything is calculated on your device — nothing you enter is uploaded, and your project is saved only in your own browser.
Estimate your tiles in seven steps
- Choose unitsPick metric (m, mm, kg) or imperial (ft, in, lb); every value converts when you switch.
- Add a roomAdd a room for each area you're tiling — the calculator consolidates them into one shopping list.
- Enter the room dimensionsType the room's width and length; the calculator works out the floor area for you.
- Set the tile size and patternEnter the tile width and length and choose the layout pattern, which sets the waste allowance.
- Enter tiles per boxRead the tiles-per-box figure off the packaging so the box count is accurate.
- Check grout and adhesiveSet the joint width and bag sizes, and turn adhesive on, to complete the materials list.
- Read the results, export or printCheck the boxes, grout and adhesive, then export to CSV or print the shopping list.
Pattern waste: why a straight grid and herringbone differ
Every tiling job loses some tiles to cuts at the walls and around fixtures, plus the odd breakage. How much you lose depends mostly on the layout: a straight grid wastes little, while diagonal and herringbone layouts cut more tiles at the perimeter and need more spares.
The calculator sets the waste allowance from the pattern you choose, using the typical ranges below, and you can override it for a tricky room. Bigger tiles in a small or irregular room push waste up; a simple rectangle pushes it down.
| Pattern | Typical waste | When it applies |
|---|---|---|
| Straight / grid | 5–10% | Tiles run square to the walls; the simplest, lowest-waste layout. |
| Brick / offset | 5–10% | Rows offset by a half or third; similar waste to a straight grid. |
| Diagonal 45° | 13–18% | Tiles turned 45°; many triangular cuts at the perimeter. |
| Herringbone | 15–20% | Interlocking zig-zag; the most cutting and the most spares. |
| Complex or small rooms | +5% | Add to any pattern for L-shapes, lots of fixtures, or large tiles in a small space. |
Grout and adhesive — from geometry, not guesswork
Most calculators quote grout as “one bag per X m².” This one works it out from the actual joint geometry — tile size, joint width and joint depth — which is far more accurate across different tile formats, and then rounds up to whole bags.
Adhesive (thin-set) is estimated from a coverage rate per square metre, which depends on the trowel notch size; the default suits a typical floor tile. Both are planning estimates — always confirm against your product's data sheet.
The numbers in the results come from these formulas.
Tiles and boxes
tiles = floor area ÷ tile area × (1 + waste); boxes = ⌈ tiles ÷ tiles-per-box ⌉- Floor area is width × length; tile area is tile width × length.
- Waste comes from the layout pattern unless you override it; boxes always round up.
Grout (from joint geometry)
grout (kg/m²) = (A + B) / (A × B) × C × D × ρ- A and B are the tile length and width, C the joint width and D the joint depth, all in mm; ρ is the grout density (≈ 1.6 kg/L).
- Total grout = kg/m² × floor area; bags round up. This is exact for any tile format, unlike a flat “bag per m²”.
Adhesive (thin-set)
adhesive = coverage rate × floor area; bags = ⌈ adhesive ÷ bag size ⌉- The coverage rate (kg/m²) depends on the trowel notch; the default suits typical floor tiles.
- Adhesive is optional — turn it off if you're only estimating tiles and grout.
Worked examples
Each example reproduces what the calculator returns, so you can check the method by hand. Figures use the calculator's defaults — 600 × 600 mm tiles, 4 per box, 3 mm joints, 10 mm thick — unless stated.
Each example reproduces the calculator's output for the given inputs.
Tiles for a 4 m × 5 m kitchen
Metric · straight grid- Given
- Room 4 m × 5 m = 20 m²
- Tile 600 × 600 mm (0.36 m²), 4 per box
- Straight grid (10% waste), 3 mm joints, 10 mm thick
- Formula
tiles = area ÷ tile area × (1 + waste); boxes = ⌈ tiles ÷ per-box ⌉- Steps
- Tiles to cover: 20 ÷ 0.36 = 55.6
- With 10% waste: 55.6 × 1.10 = 61.1 → 62 tiles
- Boxes: ⌈ 62 ÷ 4 ⌉ = 16 boxes (64 tiles) → 2 spare
- Grout: 0.16 kg/m² × 20 = 3.2 kg → one 5 kg bag
- Result
- Buy 16 boxes (64 tiles) and one 5 kg grout bag — about 2 spare tiles
Tiles for a 12 × 12 ft room
Imperial · straight grid- Given
- Room 12 ft × 12 ft = 144 ft²
- Tile 24 × 24 in (4 ft²), 4 per box
- Straight grid (10% waste)
- Formula
tiles = area ÷ tile area × (1 + waste); boxes = ⌈ tiles ÷ per-box ⌉- Steps
- Tiles to cover: 144 ÷ 4 = 36
- With 10% waste: 36 × 1.10 = 39.6 → 40 tiles
- Boxes: ⌈ 40 ÷ 4 ⌉ = 10 boxes (40 tiles) → 0 spare
- Result
- Buy 10 boxes (40 tiles) — no spare, so consider one extra box for repairs
Same kitchen, laid herringbone
Metric · herringbone- Given
- Room 4 m × 5 m = 20 m²
- Tile 600 × 600 mm (0.36 m²), 4 per box
- Herringbone (18% waste)
- Formula
tiles = area ÷ tile area × (1 + waste)- Steps
- Tiles to cover: 20 ÷ 0.36 = 55.6
- With 18% waste: 55.6 × 1.18 = 65.6 → 66 tiles
- Boxes: ⌈ 66 ÷ 4 ⌉ = 17 boxes (68 tiles) → 2 spare
- Result
- Herringbone needs 17 boxes versus 16 for a straight grid — the pattern alone adds a box
Common mistakes to avoid
Ordering by area alone. Tiles come in boxes, so 20 m² of tile is really “how many whole boxes cover 20 m² plus waste” — always round up to boxes, not square metres.
Using the same waste for every layout. A straight grid might lose 10%; herringbone can lose 18–20%. Match the allowance to the pattern or you'll run short on the cuts.
Guessing the tiles-per-box. It varies enormously by tile size and brand — a 600 × 600 box might hold 4 tiles, a 300 × 300 box 11. Read it off the packaging.
Ordering across several dye lots later. Buy the whole job — including spares — in one go so the colour matches, and keep a few leftover tiles for future repairs.
Forgetting the consumables. Grout and adhesive are easy to leave off the list; the calculator adds both so you don't make a second trip.
Frequently asked questions
Short answers to the questions people most often ask about estimating tile, grout and adhesive with this calculator.
How many tiles do I need?
Divide the floor area by the area of one tile, then add a waste allowance for cuts and breakages. In short: tiles = area ÷ tile area × (1 + waste). For a 20 m² room with 600 × 600 mm tiles that's about 56 tiles, or 62 with 10% waste. The calculator does this as you type and rounds it up to whole boxes.
How many boxes of tile should I buy?
Divide the tiles you need (including waste) by the number of tiles in a box and round up. The tiles-per-box figure is printed on the packaging and varies a lot by tile size, so always check it — the calculator uses your value to work out the boxes and the spare tiles.
How much waste should I allow for tiling?
For a straight or brick layout, 5–10% is typical. Diagonal layouts need about 13–18% and herringbone 15–20% because they cut more tiles at the edges. Add roughly 5% more for L-shaped or small rooms, lots of fixtures, or large-format tiles. The calculator sets a sensible default from the pattern and lets you override it.
How much extra tile for a diagonal pattern?
A 45° diagonal layout typically wastes 13–18% because the perimeter is full of triangular cuts, versus 5–10% for a straight grid. Choose the diagonal pattern and the calculator raises the allowance automatically; bump it up further for a small or irregular room.
How much extra tile for herringbone?
Herringbone is the most cutting-intensive common layout, so allow 15–20% waste — more than double a straight grid. In a 20 m² kitchen with 600 mm tiles that's the difference between 16 and 17 boxes. Select the herringbone pattern and the calculator applies 18% by default.
How much grout do I need?
Grout depends on the tile size, joint width and joint depth, not just the area. The calculator uses grout (kg/m²) = (A + B) / (A × B) × C × D × ρ, with the tile and joint dimensions in mm and density ρ ≈ 1.6 kg/L, then multiplies by the floor area and rounds up to bags. Wider joints, deeper joints and smaller tiles all use more grout.
How much tile adhesive do I need?
Adhesive (thin-set) is estimated from a coverage rate per square metre, which depends on the trowel notch size — around 4 kg/m² is typical for floor tiles with a 6 mm notch. The calculator multiplies the rate by the floor area and rounds up to bags. Larger tiles and bigger notches use more; always check the product's data sheet.
How many tiles are in a box?
It varies a lot by tile size and brand: a 600 × 600 mm box often holds 4 tiles (about 1.44 m²), while a 300 × 300 mm box might hold 11. There's no universal number, so read it off the packaging and enter it — the calculator flags this as the assumption that most affects your box count.
Can I calculate several rooms at once?
Yes. Add a room for each area you're tiling and the calculator consolidates them into a single shopping list — it sums the tiles across rooms before rounding up to boxes, so you don't over-buy from per-room rounding. Grout and adhesive are totalled the same way.
Does it work in metric and imperial?
Yes. Enter rooms in metres or feet and tiles in millimetres or inches, with grout and adhesive in kilograms or pounds. Switch the unit toggle at any time and every input and result converts, so it suits both EU and US tiling jobs.
Can I export or print the result?
Yes. Export CSV downloads the breakdown for Excel, Google Sheets or Numbers, and Print / PDF produces a clean shopping list with the rooms, areas, tiles, boxes, grout and adhesive — handy to take to the tile shop.
Is the calculator private?
Yes. Every calculation runs in your browser — nothing you enter is uploaded to a server. Your project is saved only in your own browser's local storage, so you can close the tab and return to it later.