Concrete Calculator (cement, sand, aggregate)
Work out cement bags, sand and aggregate for a slab, floor, beam or footing. Enter length, width, thickness and pick the mix (M10, M15, M20).
Quick answer
3 × 3 m, 15 cm thick, M15: 9 bags of cement.
How it is calculated
- Wet volume = length × width × thickness = 3 × 3 × 0.15 = 1.35 m³.
- Dry volume = wet × 1.54 (for voids and shrinkage).
- Split by the mix ratio, e.g. M15 = 1:2:4. One 50 kg cement bag ≈ 0.0347 m³.
Worked example
A 3 m × 3 m floor, 15 cm thick, in M15 (1:2:4). Wet volume 1.35 m³. You need cement 9 bags, sand 21 cft and aggregate 42 cft.
| Length | 3 m |
| Width | 3 m |
| Depth / thickness | 0.15 m |
| Mix | M15 (1:2:4) |
| Cement bags (50 kg) | 9 bags |
| Wet volume | 1.35 m³ |
| Sand | 21 cft |
| Aggregate | 42 cft |
Formula
Dry volume = wet × 1.54; 1 bag cement = 0.0347 m³
wet = Ln×Wd×Dp dry = wet×1.54 Cement bags (50 kg) = ceil(dry/Mx/0.03472) Wet volume = wet Sand = dry×((Mx-1)/3)/Mx×35.3147 Aggregate = dry×(2×(Mx-1)/3)/Mx×35.3147
Good to know
- RCC slabs and columns usually use M20 or higher.
- Keep about 5% extra for wastage on site.
Questions people ask
How much cement for 1 m³ of M20?
About 8 bags (50 kg).
Why multiply by 1.54?
Dry materials pack tighter once water is added, so about 54% more is needed.
Measurements in feet?
Divide feet by 3.281 to get metres: 10 ft ≈ 3.05 m.
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Updated 13 Nov 2026 · Desktop N Calculator v1.2.0