Cement Ratio Guide: Understanding Mix Proportions

A mix ratio expresses the proportion of cement, sand, and coarse aggregate in a concrete mix by volume. A 1:2:4 ratio means one part cement to two parts sand to four parts aggregate — seven total parts, of which cement is one-seventh.

The ratio you choose depends entirely on what you're building. Lean mixes like 1:3:6 suit non-structural fill and blinding layers. General-purpose structural work commonly uses 1:2:4. High-strength applications — footings, columns, and load-bearing slabs — often move to 1:1.5:3 or a designed mix specified by a structural engineer. Always check local building code requirements before choosing a ratio for load-bearing work.

To convert a ratio into a material order, you first need your target wet (poured) volume. Multiply that by 1.54 to account for the volume lost as dry, loose materials compact and fill with water during mixing — this is the standard "dry volume" conversion factor. Divide the resulting dry volume among the ratio's parts, and convert the cement portion into bags using the standard 0.035 m³ per 50kg bag.

Getting the ratio wrong in either direction has real cost: too lean and the concrete under-performs structurally; too rich and you're paying for cement you didn't need. When in doubt on anything load-bearing, the ratio is a question for a structural engineer, not a calculator.