worldofcalcsConcrete Calculator
Concrete volume
125 cft · 3.54 m³
Cement
29 bags
28.56 bags of 50 kg
Sand
52.5 cft
1.49 m³
Aggregate (20 mm)
105 cft
2.97 m³
Water
714 L
At a water-cement ratio of 0.5
How is concrete quantity calculated?
First find the volume of concrete: length × width × thickness. Dry materials pack down when mixed with water, so the dry volume is about 1.54 times the wet volume. The mix ratio then splits that dry volume between cement, sand and aggregate. This calculator does it for the nominal mixes M10, M15, M20 and M25, and gives sand and aggregate in cft, as they're sold in India.
Concrete material formulas
Dry volume = wet volume × 1.54 · Cement = dry × c ÷ (c + s + a) ÷ 0.0347 m³ per bag · Sand = dry × s ÷ (c + s + a) · Aggregate = dry × a ÷ (c + s + a)
c : s : a is the mix ratio, such as 1 : 1.5 : 3 for M20. A 50 kg bag of cement is 0.0347 m³, and 1 m³ is 35.3 cft.
Good to know
- M20 (1 : 1.5 : 3) is the minimum grade for reinforced concrete slabs, beams and columns in homes under IS 456. M15 and M10 are used for floors, PCC and foundation beds.
- For bigger jobs, ready-mix concrete is batched by weight and is usually more consistent than site mixing.
- Add 2–5% for wastage and uneven ground, more for footings dug in soil.
- Too much water weakens concrete. Keep the water-cement ratio around 0.45–0.5 and cure the concrete with water for at least 7 days (10 or more in hot weather).
- This uses nominal mixes. Larger projects use a design mix tested in a lab, which can need less cement.
Worked example: a 20 × 15 ft slab, 5 inches thick, in M20
- Volume: 20 × 15 × 5/12 = 125 cft, or 3.54 m³
- Dry volume: 3.54 × 1.54 = 5.45 m³
- M20 is 1 : 1.5 : 3, which adds up to 5.5 parts
- Cement: 5.45 ÷ 5.5 = 0.99 m³ ÷ 0.0347 = 28.6, so 29 bags
- Sand: 52.5 cft; aggregate: 105 cft; water about 714 litres
Materials for 1 m³ of concrete
Cement, sand and aggregate for one cubic metre of each nominal mix.
| Grade | Mix | Cement bags | Sand (cft) | Aggregate (cft) |
|---|---|---|---|---|
| M10 | 1 : 3 : 6 | 4.44 | 16.3 | 32.6 |
| M15 | 1 : 2 : 4 | 6.34 | 15.5 | 31.1 |
| M20 | 1 : 1.5 : 3 | 8.07 | 14.8 | 29.7 |
| M25 | 1 : 1 : 2 | 11.10 | 13.6 | 27.2 |
Based on a dry volume factor of 1.54, without wastage.