AAC is ordered by thickness and priced per block or per cubic metre, so a house's block order is really two or three separate orders. The calculation is the same for each.
The Method
- Group walls by thickness — external (usually 8 inch), internal (6 inch), wet areas (4 inch).
- Total length of each group from the plan.
- Height from floor to beam soffit (not floor to floor).
- Gross area = length × height.
- Subtract openings (doors, windows, ventilators) in that wall group.
- Blocks = net area ÷ 0.12 m² (or net sq ft × 0.77).
- Add 3–5% for cutting at openings and corners.
Worked Example: Single-Floor 1,000 sq ft House
| Wall group | Length | Height (to beam) | Gross area | Openings | Net area | Blocks (+5%) |
|---|---|---|---|---|---|---|
| 8 inch external | 130 ft | 9 ft | 1,170 sq ft | 180 sq ft | 990 sq ft | 990 × 0.77 × 1.05 ≈ 800 |
| 6 inch internal | 110 ft | 9 ft | 990 sq ft | 120 sq ft | 870 sq ft | 870 × 0.77 × 1.05 ≈ 705 |
| 4 inch toilets | 40 ft | 9 ft | 360 sq ft | 40 sq ft | 320 sq ft | 320 × 0.77 × 1.05 ≈ 260 |
| Total | ≈ 1,765 |
Add parapets, sunshade cheeks and any half-height walls, and the total for such a house commonly lands around 2,000–2,500 blocks. A G+1 roughly doubles it.
Convert to Cubic Metres
Blocks per m³: about 42 (8 inch), 56 (6 inch), 83 (4 inch).
From the example: 800 ÷ 42 + 705 ÷ 56 + 260 ÷ 83 ≈ 19.0 + 12.6 + 3.1 = about 34.7 m³ — useful when comparing plant prices per m³.
Adhesive
Use the manufacturer's coverage per bag for each thickness. Thin-bed adhesive uses a fraction of the material that cement mortar would.
The Short Version
Net wall area by thickness ÷ 0.12 m² (or × 0.77 per sq ft), plus 5%. Order each thickness separately and compare prices per m³.
