Tile jobs have three material lines that behave very differently: the tile, the bed it sits in, and the grout between. Each needs its own calculation.
Tiles: work in modules
Each tile plus its share of joint covers (tile width + joint) × (tile length + joint). Divide the area by this module, not by the bare tile size. On small tiles with wide joints the difference is several percent.
Then add waste: 10% for a straight lay, 15% for diagonal, and more for large-format tiles where a single breakage costs a lot. Buy whole boxes from the same batch.
Adhesive: it's all about the notch
The trowel notch sets the bed thickness, and bigger tiles need bigger notches for full coverage.
| Tile size | Typical notch | Coverage |
|---|---|---|
| Mosaic / small wall tile | 4–6 mm | ~2.5–3 kg/m² |
| Up to 12" / 300 mm | 6–8 mm | ~3–4.5 kg/m² |
| Large format | 10–12 mm | ~5.5–6.5 kg/m² |
Back-buttering large tiles adds roughly 30%.
Grout: joints, not area
Grout fills the joint volume: area × (length + width) ÷ (length × width) × joint width × depth. That's why mosaics use many times more grout per area than large tiles. The grout calculator applies this directly.
Prep
- Leveller where the floor is out of flat
- Tile backer board or uncoupling membrane
- Waterproofing in wet areas
- Primer for the substrate
- Movement joints and trims
This guide is general information for estimating. It is not engineering, legal or tax advice. Check the Building Regulations and Building Control for your project.