Concrete Mix Ratio Calculator
Calculate cement bags, sand, aggregate, and water for any target wet volume of concrete using IS 456 grades or a custom mix ratio.
How this works
We follow the IS 456 dry-volume rule. Loose sand and aggregate occupy more space than placed concrete, so the dry-material volume is 1.54 × the wet volume:
dryVol = wetVol × 1.54
parts = c + s + a
cementVol = dryVol × c / parts
sandVol = dryVol × s / parts
aggVol = dryVol × a / parts
cementBags = cementVol / 0.0347 (50 kg bag)
waterL = cementVol × 0.5 × 1000 (w/c ≈ 0.5)Wastage is applied uniformly: output = base × (1 + wastagePct / 100). Cement bags are rounded up after the wastage factor since you can't buy a fractional bag.
Worked example
10 m³ of M20 concrete (ratio 1:1.5:3) at 5% wastage:
- Dry volume =
10 × 1.54 = 15.4 m³ - Cement volume =
15.4 × 1 / 5.5 ≈ 2.80 m³ - Cement bags ≈ 2.80 / 0.0347 × 1.05 ≈ 85 bags
- Sand =
15.4 × 1.5 / 5.5 × 1.05 ≈ 4.41 m³ - Aggregate =
15.4 × 3 / 5.5 × 1.05 ≈ 8.82 m³ - Water ≈ 2.80 × 0.5 × 1000 × 1.05 ≈ 1,470 L
Sources
- IS 456:2000 §9.2 (Nominal Mix Concrete) and §10.3 (Production of Concrete — bulking allowance)
FAQ
Why is the dry volume 1.54 times the wet volume?
IS 456:2000 §10.3 specifies a 54 percent bulking allowance when sizing dry materials. Loose sand and coarse aggregate occupy a larger volume than they do once mixed with cement paste, because the cement paste fills the voids between particles. Multiplying the wet (placed) volume by 1.54 gives the equivalent dry volume of constituents you actually need to procure.
What grade should I use for slabs, beams, and columns?
M20 (1:1.5:3) is the standard residential structural grade for slabs, beams, and columns in non-coastal regions. M25 (1:1:2) is used in earthquake zones and for taller buildings. M15 (1:2:4) is acceptable for non-structural elements and PCC. M10 and lower are lean concretes used as blinding and mass fill. Always cross-check against the structural drawing — the engineer of record is the binding source.
How many bags of cement are in one cubic metre?
One 50 kg bag of OPC has a loose bulk volume of about 0.0347 m³ (50 kg ÷ 1440 kg/m³). So one cubic metre of cement holds roughly 28.8 bags. For an M20 mix at the IS 456 ratio of 1:1.5:3, one cubic metre of placed concrete needs about 8 bags of cement. The calculator does this conversion automatically and rounds up so you can place a procurement order directly.
Why does the calculator add a wastage percentage?
Field practice always loses material to spillage, mixer residue, formwork loss, and over-pour at the edges. A 5 percent wastage allowance is the conservative default that procurement teams use. Bump it to 10 percent for small site-mix pours where wastage is higher relative to the batch size, or pull it down to 2–3 percent for ready-mix where the supplier absorbs most of the loss.
How is water requirement estimated?
We use a water-to-cement ratio of 0.5 by volume — the conventional field rule for nominal-mix concrete giving a workable consistency. The water litres come out as cementVol × 0.5 × 1000. For a designed mix or for higher strengths (M25 and above), the actual w/c ratio is determined by an IS 10262 mix design and is typically lower (0.4–0.45). Treat this as a planning estimate, not a batching instruction.
Can I enter a custom mix ratio instead of using a grade?
Yes. Switch to the custom ratio mode and enter cement, sand, and aggregate parts directly — the calculator runs the same dry-volume and wastage logic on whatever ratio you supply. This is useful for designed mixes from your structural consultant, for legacy ratios used in older projects, or for non-standard mortars.