Blinding = (footing length + 2 × margin) × (footing width + 2 × margin) × thickness × number of footings. Ten 1.5 × 1.5 m footings with 100 mm margin and 50 mm of 1:3:6 blinding need 28.9 m² × 0.05 = 1.45 m³, or 1.59 m³ with 10%, about 7 bags of cement.
Area = (L + 2m) × (W + 2m) × n (or the known area)
Volume = area × thickness × (1 + wastage %)
Worked example
Ten footings 1.5 × 1.5 m, 100 mm margin, 50 mm thick, 1:3:6, 10% wastage:
- Area = 1.7 × 1.7 × 10 = 28.9 m²
- Volume = 28.9 × 0.05 = 1.445 m³; with 10% = 1.59 m³
- Cement ≈ 7.0 bags, sand 0.73 m³, aggregate 1.47 m³
| Footing |
Blinding area |
Volume |
| 1.0 × 1.0 m |
1.44 m² |
0.072 m³ |
| 1.5 × 1.5 m |
2.89 m² |
0.145 m³ |
| 2.0 × 2.0 m |
4.84 m² |
0.242 m³ |
| 2.5 × 2.5 m |
7.29 m² |
0.365 m³ |
| 3.0 × 3.0 m |
10.24 m² |
0.512 m³ |
Frequently Asked Questions
What is blinding concrete?
A thin layer of lean concrete, usually 50–75 mm of 1:3:6 or 1:4:8 (C10 or C15), placed on the excavated ground to give a clean, level surface for setting out, formwork and reinforcement.
How far should blinding extend beyond the footing?
Usually 75–150 mm each side so the formwork sits on blinding. Your drawings may show a specific margin.
How much cement is needed for blinding?
About 4.4 bags (50 kg) per cubic metre of 1:3:6 and 3.4 bags for 1:4:8, by the 1.54 dry-volume method.
