How to use the tile calculator
- Choose metric or imperial. Tile sizes are in centimetres or inches, joints in millimetres or inches.
- Add each floor or wall area you will tile as a rectangle.
- Enter the tile size, the grout joint width and a waste allowance.
- Optionally enter tiles per box and a price, and tick grout or adhesive to estimate those too.
- Check the layout preview and print the plan.
How the estimate is worked out
- Area to tile = length × width for each area, added together, then increased by the waste allowance.
- Space per tile = (tile length + joint) × (tile width + joint).
- Tiles = area with waste ÷ space per tile, rounded up. Boxes = tiles ÷ tiles per box, rounded up.
- Grout = joint volume per square metre × joint depth × grout density × area with waste.
- Adhesive bags = area with waste ÷ coverage per bag, rounded up.
Worked example
A kitchen floor 3.6 × 3.0 m is tiled with 600 × 300 mm tiles, 3 mm joints and a 10% waste allowance. Tiles come 8 to a box.
- Area: 10.8 m². With 10% waste: 11.88 m².
- Space per tile: 603 × 303 mm = 0.182709 m², so 5.473 tiles per m².
- 11.88 × 5.473 = 65.02, so you need 66 tiles, which is 9 boxes (72 tiles).
- Grout 9 mm deep at 1.6 kg/L: 0.2135 kg per m² × 11.88 m² = 2.54 kg.
- Adhesive at 4 m² per bag: 11.88 ÷ 4 = 2.97, so 3 bags.
Choose Try an example above (with metric selected) to load these numbers.
Assumptions and limitations
- Areas are rectangles and tiles are laid in a straight grid. Offset (brick) patterns use about the same number of tiles; diagonal and herringbone need a larger waste allowance.
- The tile count is based on area. Small offcuts are not reused, which the waste allowance is meant to cover.
- Grout and adhesive estimates depend on the product figures you enter. Mix and use them as the maker instructs.
- Trims, edging strips, spacers, primer, sealant and waterproofing are not included.
Frequently asked questions
How many extra tiles should I buy?
Around 10% extra is common for a straight grid in a simple room. Diagonal and herringbone layouts, large-format tiles, rooms with many corners and natural stone usually need 15% or more. Keeping a few spare tiles from the same batch also makes future repairs much easier.
What grout joint width should I use?
Follow the tile maker’s recommendation. Rectified porcelain is often laid with 2–3 mm (about 1/16–1/8 in) joints, while handmade or rustic tiles often need wider joints. Floor tiles commonly have slightly wider joints than wall tiles.
How is the amount of grout worked out?
Grout fills the joints between tiles, so the amount depends on the joint width and depth (usually the tile thickness) and the tile size: smaller tiles have more joint per square metre. The calculator works out the joint volume per square metre and multiplies it by the grout’s density. The density is pre-filled with 1.6 kg per litre, a typical figure for cement-based grout, but you can change it to match your product’s data sheet.
Where do I find adhesive coverage?
Tile adhesive bags give a coverage figure that depends on the trowel notch size, for example “a 20 kg bag covers about 4 m² with a 10 mm notch”. Larger tiles need a bigger notch and more adhesive. Use the figure for the notch you will use.
Can I use this for walls?
Yes. Enter each wall area as width × height of the part you will tile, for example a splashback or the area around a bath. Don’t include windows or areas you won’t tile.
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