TryBuildCalcSlab Concrete Material Calculator (Slab Cement, Sand & Aggregate)
Estimate slab concrete materials instantly.
🕒 Last updated: August 17, 2026
Inputs
Cost
For a 11.15 m² footprint (M20, 1:1.5:3), you need approximately 1.49 m³ (52.5 cft) of concrete — 12 cement bags.
Concrete Volume
Wet volume (before wastage): 1.416 m³
Dry volume: 2.180 m³
Final quantity (with wastage): 1.49 m³ (52.5 cft)
Materials
Cement: 12.0 bags (600 kg) — buy 12 bags
Sand: 0.62 m³ (22.1 cft)
Aggregate: 1.25 m³ (44.1 cft)
Water (approx., w/c 0.50): 300 litres
Order Summary — Theoretical vs. Order Quantity
| Material | Theoretical | Order Quantity |
|---|---|---|
| Concrete | 1.42 m³ | 1.49 m³ (52.5 cft) |
| Cement | 11.4 bags | 12 bags (whole) |
| Sand | 0.60 m³ | 0.62 m³ |
| Aggregate | 1.19 m³ | 1.25 m³ |
| Water (approx.) | 286 litres | 300 litres |
Theoretical = before wastage. Order Quantity = after your 5.0% wastage allowance (cement rounded up to a whole bag).
Assumptions Used
Dry volume factor: 1.54 | Cement bag: 50 kg / 0.0347 m³ | Nominal mix ratio (not a lab-designed mix) | Water quantity uses a typical water-cement ratio for this mix — approximate, and not a substitute for a lab-verified mix design | Wastage applied once to the final wet volume, cement, sand, and aggregate figures.
Looking for the verification checklist, reference tables, tips, or common mistakes?See the complete Concrete Cement Calculator.
Slab concrete material estimate
This page is pre-filled for a typical residential slab — 12 ft × 10 ft in plan, 5 inch thickness, M20 (1:1.5:3) mix — a common combination for a roof or floor slab.
Edit the plan dimensions, thickness, or mix ratio above to match your actual slab, and the material breakdown updates from the active values.
- Slab volume = plan area × slab thickness — measure thickness from the finished slab, not just the formwork depth.
- M20 (1:1.5:3) is a common minimum grade for reinforced slabs; higher-load slabs may specify M25.
- Use the Concrete Footing Calculator separately for footings supporting this slab, if applicable.
Concrete Cement Formula: How Is Quantity Calculated?
Understanding how cement quantity is calculated helps in verifying estimates and improving construction material planning accuracy.
Step 1 — Concrete Volume
Wet Volume = Length × Width × Thickness
Dry Volume = Wet Volume × 1.54
Wet volume is the poured volume for slabs, footings, beams, or columns. Dry volume accounts for voids between aggregate particles, bulking of sand, and practical construction losses that disappear once the concrete is mixed and compacted.
Step 2 — Mix Ratio Distribution
Cement Volume = Dry Volume × (Cement Part ÷ Total Parts)
Sand Volume = Dry Volume × (Sand Part ÷ Total Parts)
Aggregate Volume = Dry Volume × (Aggregate Part ÷ Total Parts)
Dry volume is distributed according to the selected mix ratio — for example 1:1.5:3 (M20) or 1:2:4 (M15). Total Parts is the sum of all three ratio parts.
Step 3 — Cement Quantity Conversion
Cement Bags = Cement Volume ÷ 0.0347 m³/bag (50 kg bags)
One standard cement bag (50 kg) occupies approximately 0.0347 cubic meters. This conversion translates calculated cement volume into practical material procurement quantities.
Step 4 — Final Quantity with Wastage
Final Wet Volume = Wet Volume × (1 + Wastage %)
This final wet volume (and the wastage-adjusted cement, sand, and aggregate figures) is the practical quantity to order or batch on site — shown separately from the theoretical pre-wastage volume.
Step 5 — Approximate Mixing Water
Final Cement Weight = Final (Wastage-Adjusted) Cement Bags × 50 kg
Water (litres) = Final Cement Weight × Water-Cement Ratio
Mixing water is estimated from the final, wastage-adjusted cement quantity above — not the pre-wastage figure — using a typical water-cement ratio for the selected nominal mix (roughly 0.45 for M25 down to 0.60 for M5, since 1 litre of water weighs about 1 kg). This is a planning estimate only — actual water-cement ratio depends on aggregate moisture, workability needs, and (above M20) the project's lab-verified mix design.
Worked Example
This example walks through your current inputs above, using the same steps as the Formula section.
Input Values Used
| Input | Value | Why it is used |
|---|---|---|
| Length × width × thickness | 12ft × 10ft × 5in | Sets the wet concrete volume |
| Mix ratio / wastage | 1:1.5:3 (M20), 5% wastage | Splits dry volume into cement/sand/aggregate and adds a buffer for site losses |
Step 1 — Volume
| Calculation | Substitution | Result |
|---|---|---|
| Wet volume | 12ft × 10ft × 5in | 1.416 m³ |
| Dry volume | 1.416 × 1.54 | 2.180 m³ |
| With 5% wastage | 1.416 × 1.05 | 1.487 m³ (52.5 cft) |
Step 2 — Materials
| Material | Quantity |
|---|---|
| Cement | 12.0 bags (600 kg) — buy 12 bags |
| Sand | 0.62 m³ (22.1 cft) |
| Aggregate | 1.25 m³ (44.1 cft) |
| Water (approx.) | 600 kg × 0.50 w/c = 300 litres |
Therefore, approximately 1.49 m³ (52.5 cft) of concrete should be ordered or batched for this element, needing 12 cement bags.
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Disclaimer: This calculator provides approximate results for planning and estimation purposes only. Actual requirements may vary based on site conditions, materials, workmanship, and local building regulations. Always consult a qualified engineer, architect, or construction professional before making final decisions.