Concrete Mix Calculator — Cement, Sand & Aggregate (IS 456)

About the Concrete Mix Calculator — Cement, Sand & Aggregate (IS 456)

Find the cement, sand, coarse aggregate and water for a volume of concrete. Choose an IS 456:2000 Table 9 nominal mix (M5 to M20, proportioned by mass), a conventional site ratio such as 1 : 1.5 : 3 measured by volume, or your own ratio. You get 50 kg cement bags, sand and aggregate in kg, tonnes, cubic metres, cft and brass, and the most water the code allows.

Every result is checked against IS 456 Table 5 for the exposure and concrete type you pick — minimum cement content (adjusted for aggregate size by Table 6), maximum water–cement ratio and minimum grade — so you can see at once when a member needs a richer mix or a proper design mix. IS 456 cl. 9.3 allows nominal mixes only up to M20; M25 and above need a design mix to IS 10262.

IS 456 Table 9: nominal mix proportions

Per 50 kg bag of cement, Table 9 sets the most dry aggregate (fine + coarse together, by mass) and the most water:

• M5: 800 kg aggregate, 60 litres water
• M7.5: 625 kg, 45 litres
• M10: 480 kg, 34 litres
• M15: 330 kg, 32 litres
• M20: 250 kg, 30 litres

Fine : coarse aggregate is generally 1 : 2 by mass, kept between 1 : 1.5 and 1 : 2.5 — finer sand and larger aggregate move it towards 1 : 2.5. For average (Zone II) sand the code's example uses 1 : 1.5, 1 : 2 and 1 : 2.5 for 10, 20 and 40 mm aggregate. Amendment 3 adds that the water needed for durability may be less than the table value, so the calculator also caps the water at the Table 5 limit.

How the quantities are worked out

Table 9 and other mass mixes use the absolute-volume method of IS 10262:2019 cl. 5.7. For one 50 kg bag, each material's mass divided by its specific gravity × 1,000 gives its solid volume; add the water and divide by (1 − entrapped air). For M20 with 20 mm aggregate and w/c 0.55: 0.01587 + 0.03145 + 0.06083 + 0.0275 = 0.13565 m³, ÷ 0.99 = 0.1370 m³ per bag, so 1 m³ needs 7.30 bags. The defaults are the IS 10262 worked-example values (OPC 3.15, sand 2.65, coarse aggregate 2.74) and its Table 3 entrapped air (1.5, 1.0 and 0.8% for 10, 20 and 40 mm).

Volume ratios use the dry-volume method: dry volume = wet volume × 1.54, split in the ratio. For 1 : 1.5 : 3, cement = 1.54 ÷ 5.5 = 0.28 m³ × 1,440 kg/m³ = 403.2 kg (8.06 bags), sand = 0.42 m³ and aggregate = 0.84 m³ per m³ of concrete. The factor allows for the voids in loose materials; 1.52–1.57 is the usual range.

Cement is taken at 1,440 kg/m³ and dry sand at 1,600 kg/m³ loose (IS 875 Part 1, Table 1); coarse aggregate at 1,600 kg/m³ (IS 875 lists 1,600–1,920 kg/m³ for stone aggregate). One brass is 100 cft.

IS 456 Table 5: durability requirements (20 mm aggregate)

• Plain concrete: mild 220 kg/m³, w/c 0.60, no minimum grade · moderate 240, 0.60, M15 · severe 250, 0.50, M20 · very severe 260, 0.45, M20 · extreme 280, 0.40, M25
• Reinforced concrete: mild 300 kg/m³, w/c 0.55, M20 · moderate 300, 0.50, M25 · severe 320, 0.45, M30 · very severe 340, 0.45, M35 · extreme 360, 0.40, M40

Table 6 adjusts the minimum cement content for aggregate size: +40 kg/m³ for 10 mm and −30 kg/m³ for 40 mm. Under cl. 6.1.3 (as amended), lower grades may be used for lean concrete, foundations for masonry walls and temporary reinforced concrete. The exposure classes are described in Table 3 — for example, mild is concrete protected from the weather away from the coast, and moderate includes concrete exposed to rain or buried in non-aggressive soil.

Sources

• IS 456:2000, Plain and Reinforced Concrete — Code of Practice (with Amendments 1–3): cl. 6.1.3, 9.3, 10.2 and Tables 3, 5, 6 and 9 — scanned text on archive.org
• IS 10262:2019, Concrete Mix Proportioning — Guidelines: cl. 5.7, Table 3 and Annex A–B examples — archive.org
• IS 875 (Part 1):1987, Unit weights of building materials, Table 1 — archive.org
• Dry-volume factor 1.54: a common Indian estimating convention, editable in Material properties

Limitations

• A nominal mix is a recipe, not a guarantee of strength — only cube tests show what the concrete achieves.
• Quantities depend on your materials: bulk density, moisture (damp sand bulks up), grading and specific gravity. Use your own test values in Material properties when you have them.
• The water shown is the most allowed, not a target. Water already in damp sand and aggregate counts towards it (IS 456 cl. 10.2.5).
• Mix design for M25 and above, admixtures, fly ash or slag blends and special concretes are not covered.

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