Concrete Mix Calculator
Estimate cement, sand, gravel and water for a given concrete amount based on the mix ratio (e.g., 1:2:3) and target volume.
—
Concrete mix ratio (cement:sand:gravel)
A mix ratio is written by volume as cement:sand:gravel parts. 1:2:3 is the structural standard for fck 25 MPa and goes into slabs, beams and columns. 1:3:3 gives you non-structural concrete near fck 15 MPa, fine for subfloors and footings that won't carry much load. 1:2:4 is the old economic mix for self-construction at fck ~20 MPa. Use washed sand, either medium or coarse, and gravel graded 0, 1 or 2 by rising diameter (0 for thin slabs, 1 for most jobs, 2 for foundations). To put numbers on it, 1 m³ at 1:2:3 takes around 7 bags cement (50 kg), 0.85 m³ sand, 1.05 m³ gravel, plus about 175 L water (w/c ≈ 0.5).
Applications
This covers slabs, beams, contrapiso (subfloor), foundations and self-construction budgeting. The reference standard is NBR 12655 (concrete production and acceptance). On structural work, the mix and fck have to come from the structural designer. This calculator estimates material; it doesn't replace the design.
FAQ
Why does the sum of parts not equal the final volume? Sand settles into the gaps between gravel grains and cement fills the gaps in the sand, so the dry mix turns out less wet concrete than you'd get by adding the components up.
Which mix for slab? For homes, 1:2:3 at fck 25 MPa is the usual choice. Anything carrying heavier loads needs a mix spelled out by the designer.
Can I replace gravel 1 with gravel 0? On thin slabs (< 8 cm) you can. The concrete comes out more workable, though a touch weaker.
Related Tools
Cement and Sand Calculator
Calculate cement bags, sand and gravel for concrete, screed and mortar by ratio (1:3, 1:4, 1:6, etc.). Everything in your browser.
Wall Concrete Volume
Compute concrete volume m³ + cement/sand/gravel estimates for a wall.
Prestress Moment
Calculate the moment generated by eccentric prestressing at a section, M_p = P·e, from the prestressing force P (kN) and the tendon eccentricity e (m). When the prestressing tendon is positioned with ECCENTRICITY relative to the section centroid (usually below, in the region tensioned by loads), the prestressing force, besides axially compressing the section (P/A), generates a BENDING MOMENT equal to force times eccentricity. This prestress moment is the key to prestressed concrete's efficiency: it is OPPOSITE to the moment from external loads (self-weight, live loads), 'bowing' the member upward (camber) and producing top-fiber tension and bottom-fiber compression — exactly the opposite of what the load does. So eccentric prestressing 'pre-loads' the member against the service loading, so that when loads act, they must first CANCEL the prestress effects before tensioning the concrete. That is why prestressed beams often show camber (upward curvature) when still unloaded. The prestress moment is fundamental in computing edge stresses, camber and the optimal tendon profile along the member (which roughly follows the load moment diagram, with varying eccentricity). Enter the prestressing force and the eccentricity.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.