A tiling estimate has three parts: the tiles, the adhesive that holds them and the grout between them. Each is simple on its own, but each has a trap: tiles need waste for cuts, adhesive depends on the trowel, and grout depends on the joint and the tile size. This guide covers all three, with TAL’s figures for adhesive and grout.
Tiles
Each tile covers its own size plus half a joint on each side. So the area one tile covers = (tile width + joint) × (tile length + joint). Then:
Formula: tiles = area ÷ ((width + joint) × (length + joint)) × (1 + waste)
Waste depends on the layout, because more cuts mean more offcuts and breakage. Typical allowances, and the ones the tile calculator offers:
| Layout | Waste |
|---|---|
| Straight lay, simple room | 7% |
| Straight lay, many cuts | 10% |
| Diagonal | 15% |
| Herringbone or chevron | 20% |
Worked example: a 4.5 × 3.6 m floor (16.2 m²) in 300 × 600 mm tiles with 3 mm joints. Each tile covers 0.303 × 0.603 = 0.183 m², so 16.2 ÷ 0.183 = 88.7 tiles, or 98 with 10% waste. Tiles are usually sold by the box; divide by the number in a box and round up. If a box held eight 300 × 600 mm tiles (1.44 m²), 98 tiles would be 12.25 boxes, so 13.
Adhesive
TAL’s Goldstar 6 datasheet gives about 3 kg per m² with a notched wall trowel and about 6 kg per m² with a notched floor trowel, in 20 kg bags. TAL says these are a guide for ordering; actual use depends on the site, the backing and the tile.
For the floor above: 16.2 × 6 = 97.2 kg, so five 20 kg bags. A wall of the same area would need about 49 kg, three bags. Large tiles, uneven floors and back-buttering (spreading adhesive on the back of the tile as well) all use more; the tile adhesive calculator lets you add for back-buttering and waste.
Grout
Grout fills the joints, so the amount depends on the joint width, the tile thickness and how many joints there are per square metre. Small tiles have far more joint per square metre than large ones. The grout volume = area × (tile length + tile width) ÷ (tile length × tile width) × joint width × joint depth, and cement grout weighs about 1.6 kg per litre.
TAL Wall & Floor Grout suits joints from 2 to 8 mm and comes in 5 kg bags. For the 300 × 600 mm floor with 3 mm joints, the grout comes to under 4 kg, so one 5 kg bag. A floor of small mosaics could need several. The grout calculator works it out for your tile and joint.
Before you order
- Order all the tiles at once, and check the batch number on every box so the shade matches.
- Keep a few spare tiles for future repairs.
- Check the floor is flat and sound; adhesive is not a levelling compound. For a new screed, see the floor screed calculator.
- Choose an adhesive suited to the tile (porcelain, large-format or ceramic) and the location (wet areas, outdoors).
- Plan the layout from the centre of the room, so the cut tiles at opposite walls match and none is a thin sliver.
Walls and floors together
When a bathroom has both floor and wall tiles, estimate them separately: they are often different sizes, the walls use the lighter wall-trowel rate of adhesive, and the floor takes the heavier floor rate. Add the two adhesive totals before rounding to bags.
Wet areas
Showers and wet floors need waterproofing under the tiles and adhesive suited to wet conditions. Follow the product maker’s system for the waterproofing, the adhesive and the grout together, so their warranties apply.
This guide is general information for estimating. It is not engineering, legal or tax advice. Check SANS 10400 (the National Building Regulations) and your local municipality’s building control officer for your project.