Concrete is batched by a simple ratio of cement to sand to aggregate — 1:2:4 means one part cement, two sand, four stone. But there is a catch: when you mix dry materials with water, the fine grains slot into the gaps between the coarse ones, so the finished wet volume is smaller than the loose dry stuff you bought. To bridge that, the wet volume is scaled up by about 1.54 to a dry volume, which is then split by the ratio to give the cement bags, sand and aggregate you actually order.
Reviewed: June 19, 2026 · Author: Naveen P N, Founder — AI Calculator · Verified against: nominal-mix volume-batching practice (IS 456 grades).
The mix-ratio equations
Σ is the sum of the ratio parts (7 for 1:2:4). Cement weight comes from its bulk density of 1,440 kg/m³, and a standard bag is 50 kg, so dividing gives the bag count. Sand and aggregate stay as volumes (m³) since they are usually batched by the box or sold by the cubic metre. The richer the cement fraction, the more bags per cubic metre and the higher the strength grade.
Worked example — 1 m³ of M15 concrete
Scenario: One cubic metre of 1:2:4 (M15) concrete at a 0.5 water-cement ratio.
So one cubic metre of M15 needs about 6.3 bags of cement, 0.44 m³ of sand, 0.88 m³ of coarse aggregate and roughly 158 litres of water. Switch to the richer 1:1.5:3 (M20) and the cement jumps to ~8 bags for the same volume, while the aggregate falls slightly — more cement, more strength. Always add about 5% to the order for spillage and wastage.
Frequently Asked Questions
dry = wet × 1.54, then split by the ratio. 1 m³ of 1:2:4 → cement 0.22 m³ (6.34 bags), sand 0.44, aggregate 0.88 m³.
Mixing fills voids, so wet volume < loose dry materials. 1.54 scales wet back to the dry quantity to buy.
~6.3 bags for 1:2:4 (M15), ~8 for 1:1.5:3 (M20), ~11 for 1:1:2 (M25). Richer mix = more bags.
28-day strength in MPa: M15 (1:2:4) non-structural, M20 (1:1.5:3) slabs/footings, M25 (1:1:2) columns.
Water = cement kg × w/c (0.45–0.55). At 0.5, ~317 kg cement needs ~158 L.