Concrete material quantities: the 1.54 dry-volume factor and cement bags

Nominal-mix concrete is specified by volume ratios — cement : sand : coarse aggregate — such as 1:2:4. Turning a wet volume of concrete into dry materials needs one factor.

Why 1.54?

Dry loose materials contain voids. When water is added and the mix is compacted, the fine particles fill the voids between the coarse ones and the volume shrinks. Experience shows the dry volume needed is about 52–57 % more than the finished wet volume. The usual working value is 1.54 (EstiMatrix's default; change it per project under Tools → Dry-to-wet factors).

The method

1. Dry volume = wet volume × 1.54
2. Sum of ratio parts = 1 + 2 + 4 = 7 (for 1:2:4)
3. Cement = dry volume × 1/7, sand = × 2/7, aggregate = × 4/7

Cement bags

A 50 kg bag of cement occupies about 1.25 cft (0.0347 cum) — cement's bulk density is roughly 1,440 kg/m³. EstiMatrix uses 1 bag = 1.25 cft = 50 kg by default.

Worked example — 1 cum of 1:2:4

• Dry volume = 1.54 cum
• Cement = 1.54 / 7 = 0.220 cum = 6.3 bags (≈ 317 kg)
• Sand = 0.440 cum
• Stone chips = 0.880 cum

Worked example — 100 cft of 1:1.5:3

• Dry volume = 154 cft; parts = 5.5
• Cement = 28.0 cft = 22.4 bags
• Sand = 42.0 cft
• Aggregate = 84.0 cft

Quick reference per cum (wet)

Add wastage

Add 1.5–2.5 % for cement and 2.5–5 % for sand and aggregate depending on site handling. EstiMatrix applies wastage per material class.

Designed mixes

For concrete specified by strength (for example 25 or 40 MPa) the proportions come from the mix design, usually by weight. Use the mix design's cement content per cum rather than nominal ratios.

Mortar

Mortar uses a smaller factor — about 1.33 — because sand alone has fewer voids to fill. See brickwork estimating and plaster quantities.