KEY TAKEAWAYS
- Three steps: area in m² → × 4.3 kg (consumption at 3 mm) → × the bed factor for your tile size.
- Bed factors: 1.0 at 3 mm, 1.12 at 6 mm, 1.56 at 10 mm, 1.93 at 12 mm.
- Add 10% wastage (15% large-format), divide by 20, round up — that is the bags.
- The bed thickness comes from the tile size — that is the step most manual estimates skip.
Our Tile Adhesive Calculator does this in a second — but every estimator should be able to run the same three steps in a notebook, because the notebook version is what catches a wrong delivery at the gate. Here is the full method with nothing hidden.
Step 1 — area in square metres
Length × width for each floor or wall, summed. Working in feet? Divide square feet by 10.76. Deduct large openings (doors, full-height windows) on walls; ignore small penetrations — they disappear inside wastage.
Step 2 — multiply by the base consumption
SUMO S-series adhesives consume 4.3 kg per m² at a 3 mm bed — the datasheet figure. This is the number that would give you the optimistic shop answer ("a bag does 50 square feet"). Step 3 is what makes it true for your tile.
Step 3 — multiply by the bed factor for your tile
- Up to 150 mm tiles → 6 mm bed → × 1.12
- 150–300 mm → 8 mm bed → × 1.33
- 300–600 mm → 10 mm bed → × 1.56
- 600 mm and up, floors → 12 mm bed → × 1.93
- Large format with back-buttering → 15 mm combined → × 2.4
Then add wastage — 10% standard, 15% large-format — divide by 20 kg, and round up to whole bags.
Two worked examples
A 200 sq.ft wall in 300 × 600 ceramic
- 200 sq.ft = 18.6 m².
- 18.6 × 4.3 = 80 kg base → × 1.12 (6 mm wall bed) = 89.6 kg.
- +10% = 98.5 kg → ÷ 20 = 4.9 → 5 bags.
A 150 sq.ft floor in 800 × 800 vitrified
- 150 sq.ft = 13.9 m².
- 13.9 × 4.3 = 59.9 kg → × 1.93 (12 mm floor bed) = 115.6 kg.
- +15% large-format = 133 kg → ÷ 20 = 6.6 → 7 bags.
Why manual estimates usually come out low
Nearly always the same miss: the estimate uses the 3 mm datasheet coverage for a 600 mm tile that actually needs a 12 mm combined bed. The factor is ~1.9 — which is exactly the gap between "the shop said 5 bags" and the 9 the floor consumed. For the full coverage tables and what changes consumption on site, see our guide on what a 20 kg bag really covers; for the arithmetic done for you, the Tile Adhesive Calculator under Tools & Support runs this method with every grade built in.
