Concrete Calculator
Work out concrete volume for a slab, footing, column or wall, then get the cement, sand and aggregate quantities needed for your chosen mix — with bag counts and an optional cost estimate.
Leave Number of units, Wastage and the custom ratio boxes empty to use 1 unit, 5% wastage and the ratio shown for the selected grade.
Optional: Estimate Cost
Fill in local rates and press Calculate again to see the estimated cost above. Leave blank to skip the cost estimate.
- Dry Volume Factor: Wet (poured) concrete settles and loses volume to voids once it sets, so the dry material volume is taken as 1.54 × the wet volume, the standard allowance used in Indian practice.
- Cement Bag Volume: One 50 kg bag of cement occupies 0.0347 m³ at a bulk density of 1440 kg/m³.
- Sand & Aggregate Density: Sand is taken at 1600 kg/m³ and coarse aggregate at 1450 kg/m³ for the weight figures shown.
- Wastage: The default 5% wastage allowance covers spillage, over-excavation and uneven sub-grade; increase it for hand-mixed or difficult pours.
Reference Guide: Concrete Volume & Mix Design
1. Volume Formulas by Shape
| Shape | Formula |
|---|---|
| Slab / Footing | Volume = Length × Width × Thickness |
| Round Column | Volume = π × (Diameter / 2)² × Height |
| Square / Rectangular Column | Volume = Width × Depth × Height |
| Wall | Volume = Length × Height × Thickness |
2. Standard Concrete Mix Ratios (Nominal Mix)
| Grade | Ratio (Cement : Sand : Aggregate) | Typical Use |
|---|---|---|
| M10 | 1 : 3 : 6 | Levelling course, PCC bedding |
| M15 | 1 : 2 : 4 | PCC, light footings, flooring base |
| M20 | 1 : 1.5 : 3 | RCC slabs, beams, columns (general RCC work) |
| M25 | 1 : 1 : 2 | RCC for higher loads, water-retaining structures |
3. Material Quantity Formulas
Cement Volume (m³) = Dry Volume × Cement Ratio / Sum of Ratio
Cement (Bags) = Cement Volume / 0.0347
Sand (m³) = Dry Volume × Sand Ratio / Sum of Ratio
Aggregate (m³) = Dry Volume × Aggregate Ratio / Sum of Ratio
For M20 (1:1.5:3), the sum of ratio parts is 5.5. So for 1 m³ of wet concrete: Dry volume = 1.54 m³. Cement = 1.54 × (1/5.5) = 0.28 m³ = about 8.1 bags. Sand = 1.54 × (1.5/5.5) = 0.42 m³. Aggregate = 1.54 × (3/5.5) = 0.84 m³.
4. Water-Cement Ratio
A water-cement ratio of 0.45 to 0.50 is typical for structural RCC work. This calculator uses 0.45 to estimate mixing water: Water (litres) = Cement weight (kg) × 0.45. Site conditions, aggregate moisture and workability requirements may call for adjustment; always follow your project's approved mix design over a nominal-mix estimate for critical structural elements.
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