Concrete Calculator
Calculate cement, sand, and aggregate quantities for your concrete mix.
Construction
Concrete Calculator
Generated on April 24, 2026
Slab Dimensions (meters)
Mix Composition
Volumetric proportions for your chosen mix (1:2:4 (M15)). Total dry volume: NaN m³.
Step-by-step calculation
Formula
Wet vol = L × W × H. Dry vol = wet × factor. Part vol = dry × (part ÷ Σparts).
- 1Wet volume = NaN × NaN × NaN = NaN m³
- 2Dry volume = wet × 1.52 (shrinkage factor) = NaN m³
- 3Mix 1:2:4 (M15): total parts = 1 + 2 + 4 = 7
- 4Cement = NaN × (1 ÷ 7) = NaN m³
- 5Sand = NaN × (2 ÷ 7) = NaN m³
- 6Aggregate = NaN × (4 ÷ 7) = NaN m³
- 7Cement bags (50 kg ≈ 0.0347 m³) = NaN ÷ 0.0347 = NaN → NaN bags
?What is the Concrete Calculator?
A concrete calculator determines the exact quantities of cement (in 50 kg bags), sand, and coarse aggregate (crushed stone or gravel) you need for any concrete pour — a slab, footing, column, or beam — based on standard South Asian mix ratios (M15 = 1:2:4, M20 = 1:1.5:3, M25 = 1:1:2). It factors in the critical 'bulking' that occurs when dry ingredients are combined with water and compacted. This is essential for homeowners planning a house foundation, contractors preparing materials orders, and site engineers ensuring the mix delivers the specified strength.
The Formula
Dry cement, sand, and aggregate together occupy about 54% more volume before mixing than the final wet concrete — because water fills the voids between the dry particles and they compact together. Multiplying the wet volume (the final pour volume) by 1.54 gives the required dry volume. Each component's share is its ratio part divided by the total parts: for a 1:2:4 mix, total = 7 parts, so cement = 1/7 of dry volume, sand = 2/7, aggregate = 4/7. One 50 kg cement bag equals 0.0347 m³ — divide cement volume by this to get the bag count.
Practical Examples
A 5 × 4 × 0.15 m M20 slab (3.0 m³ wet) needs 4.62 m³ dry, split as 0.84 m³ cement (≈24 bags), 1.26 m³ sand, and 2.52 m³ aggregate.
A 3 × 3 × 0.3 m M25 foundation (2.7 m³ wet) needs roughly 0.67 m³ cement, 0.67 m³ sand, and 1.35 m³ aggregate.
A 0.3 × 0.3 × 3 m M20 column (0.27 m³ wet) needs about 2 cement bags plus proportional sand and aggregate — a small pour.
One 50 kg cement bag equals 0.0347 m³ of cement — always plan to round up when buying bags.
For every 50 kg of cement, you need roughly 25 liters of water (a water-cement ratio of 0.5 by weight) for good workability and strength.
A typical 1,000 sq ft single-story house foundation requires roughly 10–15 m³ of concrete depending on footing depth and structural design.