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Concrete Calculator

Cement bags, sand, aggregate and water for any slab — by grade, formula shown.

ConstructionCore● Free Formula shown Rates dated
Quick Answer

One cubic metre of M20 (1:1.5:3) concrete needs about 8 bags of cement, 15 cft of sand and 30 cft of aggregate before wastage. A typical 10 × 10 ft slab cast 5 inches thick therefore takes ~10 bags of cement and roughly ₹6,000–8,200 of material (as of Jul 2026). Enter your slab size and grade below for exact quantities with the full working shown.

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The Formula

Materials = dry volume (wet volume × 1.54) split in the grade's cement : sand : aggregate ratio, + published wastage

Mixing and compacting squeezes the air and water out of the loose ingredients, so you need about 54% more dry material than the finished wet volume — that is the 1.54 factor. Cement volume converts to bags at 0.0347 m³ (1.226 cft) per 50 kg bag.

Assumptions & Wastage

  • Nominal volumetric mixes as used in Indian site practice: M7.5 = 1:4:8, M10 = 1:3:6, M15 = 1:2:4, M20 = 1:1.5:3, M25 = 1:1:2 (cement : sand : aggregate)
  • Dry volume = wet volume × 1.54, covering voids in aggregate and bulking of sand
  • One cement bag = 50 kg ≈ 0.0347 m³ at 1,440 kg/m³ bulk density
  • Water estimated at a water–cement ratio of 0.45–0.55 by weight of cement
  • Wastage is added on the computed base quantities using the published allowances below — nothing is pre-included, so do not add wastage again
  • For M25 and above, or any element an engineer has designed, use the design mix from the structural drawings — a nominal ratio is a site convention, not a design
MaterialWastage allowance
cement3%
sand10%
aggregate5%

Worked Examples

10 × 10 ft slab, 5 inches thick, M20

  1. Wet volume: 10 × 10 ft × 5 in = 41.7 cft = 1.18 m³
  2. Dry volume: 1.18 × 1.54 = 1.82 m³ (the 54% extra covers voids and bulking)
  3. Cement: 1.82 × 1/5.5 = 0.33 m³ ÷ 0.0347 m³/bag = 9.5 bags; +3% wastage → 10 bags
  4. Sand: 1.82 × 1.5/5.5 = 17.5 cft; +10% wastage = 19.2 cft
  5. Aggregate: 1.82 × 3/5.5 = 35 cft; +5% wastage = 36.7 cft
  6. Water at w/c 0.45–0.55: ≈ 214–262 litres
  7. Material cost: ₹5,641 to ₹8,289 (as of Jul 2026)

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500 sq ft roof slab (25 × 20 ft), 5 inches, M20

  1. Wet volume: 25 × 20 ft × 5 in = 208.3 cft = 5.9 m³
  2. Dry volume: 5.9 × 1.54 = 9.08 m³
  3. Cement: 9.08 × 1/5.5 = 1.65 m³ ÷ 0.0347 m³/bag = 47.6 bags; +3% wastage → 50 bags
  4. Sand: 87.5 cft; +10% wastage = 96.2 cft
  5. Aggregate: 175 cft; +5% wastage = 183.7 cft
  6. Water at w/c 0.45–0.55: ≈ 1,071–1,309 litres
  7. Material cost: ₹28,206 to ₹41,444 (as of Jul 2026)

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Rates & Model Data Used

Every number below is a range with a date — material prices in India move quickly, so always check the "as of" month before relying on a figure.

ItemRate / valueAs ofNote
Cement (OPC 43 grade)₹320–415 / bag (50 kg)Jul 2026Per 50 kg bag as listed by retail sources; no dealer page in the set states a tax basis, so GST-inclusive at 18% is inferred, not quoted — a strong inference, but an inference, and the reason this is medium rather than high. Re-baselined 2026-07-24: the band was ₹340–410 at high confidence, resting on two content farms plus official anchors that turn out to be estimating conventions rather than market evidence. Grade does not move the retail price. On the only dated price list found that quotes both grades (Bangalore, 6 Jul 2026, seven brands), five of seven price OPC 43 and OPC 53 identically to the rupee, the mean difference is −₹1.79/bag and the median is exactly zero — so OPC 53 carries this same band. No Indian government schedule prices the grades apart either: CPWD DAR 2023 carries a single grey-cement rate of ₹5,156/t and lets estimators substitute ordinary, pozzolana or slag against it, and WPI has no OPC 53 series. That is an accounting convention rather than proof about the market, but not one official source in the country supports paying more for 53. What does move the price: brand ₹75/bag (Maha ₹335 against UltraTech ₹410, same list, same day — 22%) and city ₹35/bag (ACC OPC 53 ₹395 Bangalore against ₹360 Hyderabad, 570 km apart). Against those, grade at zero is a rounding error. Bulk orders of 100+ bags take another ₹10–20/bag off. GST moved 28% → 18% on 22-09-2025 (CBIC Notification 9/2025, heading 2523, which names slag cement expressly); any bag price published before Oct 2025 is on the old regime — multiply by 1.18/1.28 = 0.9219, a 7.8% fall, before comparing. Cost check: ₹320 incl. = ₹5,424/t ex-GST against CPWD's ₹5,156/t ex-GST ex-carriage bulk Delhi (Apr 2023) = +5.2%, which leaves about 5% for carriage plus the whole dealer chain — thin, and only plausible near a plant, which is what a value brand in a southern clinker market is. Cement WPI has moved between −3% and +2% since Apr 2023, so no inflation adjustment to that anchor is warranted. Declared weaknesses: the ₹400–415 ceiling is two lines on one Bangalore page (verbatim-confirmed by three independent readers, uncorroborated elsewhere — the one corroborator refused connection), first-hand retail evidence is two southern cities plus one Delhi single-brand list, and July is near the seasonal trough since cement softens through the monsoon and firms in the Jan–Mar infrastructure season. Treat as a national indicative band and check your own market.
River sand₹60–110 / cftJul 2026Re-anchored 2026-07-25: the three content farms (HouseYog, Civiconcepts, Varna Homes) that used to back this band are struck; it now rests on two government schedules read firsthand — but be clear about what they anchor. CPWD DAR 2023 applies coarse sand (zone III, natural) at ₹1,450/cum throughout its own concrete and mortar rate analyses = ₹41/cft ex-GST, ₹43/cft incl. 5% GST (a stray basic-rate index line at ₹285/cum is an anomalous layout artifact, not the applied rate; the '₹1,450 = spirit/air-compressor' reading is a coincidental-value misread — the operative applied rate is ₹1,450). Maharashtra PWD SSR 2022-23 (p.541) gives natural/VSI/artificial sand ₹1,670/cum = ₹47/cft, crushed ₹1,200/cum = ₹34/cft, screened natural (plaster) ₹1,781/cum. So the government evidence pins an EX-GST, EX-CARRIAGE, AT-SOURCE rate of ~₹41–47/cft (~₹43–50 incl. GST at yard) — and that is ALL it pins. The ₹60 floor is that yard rate plus a minimum ~₹15/cft lead (matching delivered Delhi ≈ ₹50–65); it is lowered from ₹70, which came only from the now-struck per-tonne blog quotes. The ₹110 ceiling is deliberately NOT re-sourced — no primary or retail anchor exists above ₹70 now — and the whole upper half is extrapolation (source rate + heavy lead + retail margin + documented 30–50% mining-ban and monsoon spikes). That is exactly why this is medium, not high, and why the carriage bridge from source to delivered is a fitted, unverified step, disclosed as such. Do not cite the schedules as proof of the delivered band; they anchor only the floor. South metros (Bangalore/Chennai/Hyderabad) sit at the ceiling and above, North plains and near-river Maharashtra at or below the floor; transport adds ₹15–40/cft. Unit exactness is the classic sand failure: confirm cft vs brass (1 brass = 100 cft = 2.83 cum) vs tonne vs truckload and whether transport is in the quote; 1 cum = 35.3147 cft. Density (resolved, unchanged): 22–24 cft/t (1,470–1,600 kg/m³) from IS 2386 Pt III, classical tables and trade 1 brass ≈ 4.5 t — do NOT cite IS 383 for density, it grades aggregate, it does not weigh it. GST 5% (natural sand HSN 2505), asserted from the standing schedule and NOT re-verified against a CBIC notification this pass — flagged. State sand portals (Telangana TGMDC, AP) are JS booking apps that expose no static notified rate.
Coarse aggregate (20 mm)₹35–55 / cftJul 2026Delivered retail; ex-supplier ₹700–900/tonne (~₹32–41/cft; 1 cft ≈ 45 kg). Long lead distances push delivered price toward ₹68/cft. 10 mm runs ₹2–5/cft above 20 mm. Official anchor (verified 2026-07): CPWD DAR 2023 20 mm single-size ₹1,425/cum = ₹40.3/cft ex-GST ex-carriage (Delhi, Apr 2023) — mid-band once carriage and GST are added; lifted to high. Primary-minerals WPI +12% YoY (Apr 2026): extraction costs are rising.

How to Use This Calculator

  1. Measure the element. Length and width in feet, thickness in inches. For odd shapes, split into rectangles and run the calculator once per piece.
  2. Pick the grade. M20 for residential slabs, beams and columns; M10/M7.5 for levelling PCC; M25+ only from a structural design.
  3. Read the quantities. Cement is rounded up to whole bags. Sand and aggregate are in cft, the unit suppliers quote in — 100 cft is 1 brass.
  4. Check the working. Every step is shown under the result, and the rates used are dated in the table below — verify any number by hand or against your contractor's estimate.

Frequently Asked Questions

How many cement bags are needed for 1 m³ of M20 concrete?
About 8 bags (precisely 8.07) before wastage: dry volume 1.54 m³ × 1/5.5 = 0.28 m³ of cement ÷ 0.0347 m³ per bag. With 15 cft of sand and 30 cft of aggregate, that is the standard M20 material set used across Indian estimation practice.
What is the 1.54 dry volume factor?
Loose sand and aggregate contain air voids, and sand bulks further when moist. Compacting wet concrete removes these, so producing 1 m³ of finished concrete consumes about 1.54 m³ of loose dry ingredients. Site practice uses 1.52–1.57; this calculator uses 1.54 and shows it in the working.
Which concrete grade should I use for a house slab?
M20 (1:1.5:3) is the standard for residential slabs, beams and columns, and the minimum grade IS 456 permits for reinforced concrete. M10 or M7.5 serve as plain levelling concrete below footings. If your structural drawings specify M25 or higher, follow the design mix in the drawings rather than a nominal ratio.
Can I use M-sand instead of river sand in concrete?
Yes — M-sand replaces river sand one-for-one by volume in concrete and is now the default in much of South India. It is typically 15–30% cheaper (₹45–75/cft vs ₹60–110/cft for river sand as of Jul 2026), has consistent gradation, and avoids monsoon supply bans.
How much water does concrete need?
Roughly 0.45–0.55 litres per kg of cement — about 23–28 litres per bag. Less water gives stronger concrete as long as it remains workable; extra water is the most common site-made strength defect. The calculator shows the band rather than one figure because workability needs differ by element and weather.
Does this include steel reinforcement?
No — reinforcement is a separate calculation that depends on the structural design, not the concrete volume. Use the steel calculator for a thumb-rule estimate (3–4 kg per sq ft of built-up area for a full house) and your drawings for element-level bar bending schedules.
Should I mix on site or order ready-mix concrete?
For anything above roughly 5 m³ in one pour — a full roof slab, for example — ready-mix (RMC) gives better quality control and casts faster than hand mixing can keep up with. For small quantities like a few columns or a chajja, site mixing with these proportions is standard. Compare the RMC quote against the material cost this calculator shows plus labour.

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Sources & Limitations

What this calculator does not model

  • Computes nominal volumetric mixes — it is not a design-mix tool and does not check strength, durability or exposure requirements
  • One rectangular element per run; split L-shapes and add the results
  • Steel, shuttering, curing and labour are excluded — this is the concrete material only
  • Admixtures (plasticisers, waterproofers) are not modelled
  • Delivered material prices vary by state and season; the cost band uses the dated national ranges below