Cement and Sand Calculator

Concrete and mortar mix calculation

Mix ratios are given by volume. Use 1:3:3 (cement:sand:gravel) for non-structural concrete, and 1:2:3 or 1:1.5:2.5 for structural work with a defined fck. One cubic metre of residential fck 25 MPa concrete takes roughly 350 kg cement, 850 kg sand, 1050 kg gravel and 175 L water, a w/c ratio near 0.5. Since a cement bag holds 50 kg, that comes to about 7 bags per m³. For sand, go with washed medium grade for mortar and coarse for concrete; gravel runs grades 0, 1 and 2 by increasing diameter. Render mortar uses 1:3 (cement:sand). As an example, a 2 m³ slab at 1:2:3 needs about 14 bags of cement, 1.7 m³ sand and 2.6 m³ gravel.

Applications and standards

It helps estimate materials for slabs, foundations, subfloors, retaining walls and the budgeting of a renovation. The relevant Brazilian standards are NBR 12655 (concrete production and acceptance), NBR 6118 (reinforced concrete structures) and NBR 7211 (aggregates). On structural work, always follow the structural engineer's spec. The calculator gives you a rough number, not a design.

FAQ

Why does the same mix give different m³? The materials pack together once mixed, so 1 m³ of dry sand plus cement plus gravel yields less than 1 m³ of wet concrete. The calculator already factors in the typical packing.

What about water? Strength comes down to the water/cement ratio (a/c): use 0.5 for fck 25 and 0.45 for higher strength. Too much water and the concrete ends up weaker.

Is ready-mix concrete cheaper? Past 5 m³, usinated concrete usually wins on both price and consistency compared with mixing on site. Below that, people tend to mix on-site with a small mixer.