Calculate the volume of concrete for a slab, beam or column — and how many bags of cement, sand and gravel to buy.
Concrete is a mixture of cement, sand (fine aggregate), gravel (coarse aggregate) and water, in a proportion called the mix ratio. A 1:2:3 mix means one part cement, two parts sand and three parts gravel by volume — the standard for structural concrete with a compressive strength around 20-25 MPa. Different applications call for different ratios: foundations use a leaner mix like 1:3:4, while columns and beams sometimes use a richer one like 1:2:4.
This calculator multiplies the three dimensions to get the geometric volume, adds 10% for waste (spillage, forms leaking, uneven surfaces) and then divides the total by the proportions of the mix. The cement is given in 50 kg bags because that is how it is sold in Brazil. Sand and gravel are given in cubic metres because that is how they are delivered.
These are planning estimates, not structural engineering. The actual concrete strength depends on the water-cement ratio, the curing conditions, the quality of the aggregates and many other factors. For anything that bears structural load, an engineer must specify the concrete — this tool calculates quantities, not structural adequacy.
Volume = length × width × thickness. Total = volume × 1.10 (10% waste). Cement bags = total × 350 × (cement parts / sum of parts) / 50.
1:2:3 for general structural work, 1:3:4 for foundations and slabs on grade, 1:2:4 for columns and beams, 1:4:6 for non-structural applications like a garden path.
Because concrete is poured into forms that are never perfectly sealed, the ground absorbs some, and mixing and transport always lose a fraction. 10% is the standard planning buffer.
Yes — the volume in cubic metres is what you order from a concrete truck. Just ignore the bags/sand/gravel breakdown.
No. The calculation runs in JavaScript on your device.
For estimating quantities, yes. For specifying the concrete strength, mix design and reinforcement, you need a structural engineer.
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