Concrete Mix Ratio by Weight Calculator

In short A mix written 1:2:4 means buckets, not kilograms, and converting between the two is not a matter of using the same numbers. Cement, sand and aggregate have different bulk densities — around 1,440, 1,600 and 1,450 kg per cubic metre — so a mix that is 1:2:4 by volume batches at 1:2.22:4.03 BY WEIGHT. Weigh out 1:2:4 on a scale and you have mixed something else. The conversion is one step: multiply each volume part by its own bulk density and normalise to cement. Here that is 1×1,440, 2×1,600 and 4×1,450, giving 1,440:3,200:5,800, which divided through by 1,440 is 1:2.22:4.03. THE TWO RATIOS COINCIDE ONLY WHEN THE DENSITIES ARE EQUAL, and the gap between them is the density spread and nothing else. Sand is the part that moves most, because it is the densest of the three. There is a second step people skip entirely. Loose dry materials occupy considerably more space than the concrete they make, because water and the finer grains fill the voids between the coarse ones. The usual factor is 1.54: one cubic metre of finished concrete needs about 1.54 cubic metres of loose material. Miss it and you under-order by roughly a third. For one cubic metre at 1:2:4 that works out at 0.22 m³ of cement — 317 kg, or a little over six 50 kg bags — with 704 kg of sand and 1,276 kg of aggregate, about 2,297 kg of dry material in all. THE DENSITIES ARE CONVENTIONS AND YOURS WILL DIFFER. All three are editable fields on this page, because bulk density moves with grading, source and how damp the pile is; bulking in damp sand is large enough to matter on site. Weigh a known bucket of each once and the arithmetic becomes yours rather than typical. And this converts the mix you were given between two ways of measuring it — it does not tell you whether that mix is the right one for what you are pouring.