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M10 to M30 · Bags · Sand · Aggregate · Cost
Concrete Calculator
Calculate volume, cement bags, sand, and aggregate for any concrete mix grade — M10 to M30. Works for slabs, columns, beams, and footings. Enter your dimensions and get instant material quantities and cost estimate. No signup required.
Uses standard dry volume factor of 1.54. Material prices are editable. Last reviewed: May 2026.
How to Use
- 1Select the concrete mix grade — M15 for foundations, M20 for slabs and columns.
- 2Enter dimensions: length, width, and depth in feet, metres, or inches.
- 3Set your wastage percentage — 5% minimum, 10% recommended.
- 4Enter current cement, sand, and aggregate prices for a cost estimate.
- 5Review volume, cement bags, sand, and aggregate quantities instantly.
Example: Roof Slab
- Slab: 20 ft × 15 ft × 0.5 ft thick
- Mix grade: M20 (1:1.5:3)
- Wet volume: 20 × 15 × 0.5 × 0.3048³ = 0.86 m³
- Dry volume: 0.86 × 1.54 = 1.32 m³
- Wastage: 7%
Cement: ~9 bags · Sand: 0.23 m³ · Aggregate: 0.46 m³
Concrete Calculation Formulas
Wet vol = L × W × D
Dry vol = Wet vol × 1.54
Cement = (c/(c+s+a)) × Dry vol ÷ 0.035 m³/bag
Sand = (s/(c+s+a)) × Dry vol (m³)
Aggregate = (a/(c+s+a)) × Dry vol (m³)
c:s:a = mix ratio. 1 bag = 50kg = 0.035 m³.
Concrete Mix Grades — Reference
| Mix Grade | Ratio (C:S:A) | Use | Compressive Strength |
|---|---|---|---|
| M10 | 1:3:6 | Lean concrete, blinding, under-slab fill | 10 N/mm² |
| M15 | 1:2:4 | Foundations, footpaths, mass concrete | 15 N/mm² |
| M20 | 1:1.5:3 | Slabs, beams, columns — standard residential | 20 N/mm² |
| M25 | 1:1:2 | Heavy RCC, high-rise columns, retaining walls | 25 N/mm² |
| M30 | 1:0.75:1.5 | Bridges, pre-stressed structures | 30 N/mm² |
Densities used: Cement 1,440 kg/m³ (1 bag = 50 kg = 0.035 m³) · Sand 1,600 kg/m³ · Coarse aggregate 1,500 kg/m³. Standard slab thickness in Bangladesh: 4.5–5 inches (115–125mm) for residential RCC per BNBC 2020.
Concrete Calculator References & Standards
- Bangladesh National Building Code (BNBC) 2020 — concrete mix design and minimum strength requirements for RCC structures.
- IS 456:2000 (Bureau of Indian Standards) — Plain and Reinforced Concrete Code of Practice; mix ratio and dry volume factor (1.54) methodology.
- ACI 211.1 (American Concrete Institute) — Standard Practice for Selecting Proportions for Normal, Heavyweight, and Mass Concrete.
- PWD Bangladesh Schedule of Rates 2023–24 — material densities, unit weights, and concrete work quantities used as reference.
Results are estimates for material planning. Always follow your structural engineer's mix design for load-bearing members. Last reviewed: May 2026.
Concrete Tips for Bangladesh
- 1Always add 5–10% wastage — spillage, over-filling of forms, and minor cracks are unavoidable on any site
- 2Use river sand (coarse to medium grain) for structural concrete — avoid fine sea sand or dusty hill sand which weaken the mix
- 320mm aggregate is standard for slabs and columns in Bangladesh; 10mm is used for thin sections under 100mm
- 4Water-cement ratio must not exceed 0.5 for M20 and above — too much water is the single biggest cause of weak concrete
- 5Cure concrete with water for at least 14 days after casting — this significantly increases final strength and reduces cracking
- 6Use a vibrator during pouring to eliminate air pockets — hand-rodding is not sufficient for columns and thick slabs
- 7Never mix concrete in extreme heat (above 35°C) without shade or chilled water — heat accelerates setting and reduces strength
- 8Store cement bags off the ground on wooden planks, covered with plastic — a damp bag can lose 15–20% of its binding strength
Frequently Asked Questions
How does the concrete calculator work?
It calculates wet concrete volume from your dimensions (Length × Width × Depth), then multiplies by a dry volume factor of 1.54 to account for voids and compaction. The dry volume is split into cement, sand, and aggregate quantities based on your selected mix ratio. A wastage percentage is added on top. The 1.54 factor is the standard value used in civil engineering practice worldwide.
What is the dry volume factor of 1.54 and why is it used?
When dry materials (cement, sand, aggregate) are mixed with water and compacted, the mix reduces in volume. To produce 1 m³ of wet concrete, you need approximately 1.54 m³ of dry materials. This accounts for voids between particles and compaction during placing. The 1.54 factor is standard in IS 456, ACI 211, and PWD Bangladesh practice.
Which concrete mix grade should I use for a roof slab in Bangladesh?
M20 (1:1.5:3) is the standard for residential RCC roof slabs, beams, and columns per BNBC 2020 and IS 456. M15 (1:2:4) is acceptable for foundations, footpaths, and non-structural mass concrete. M25 and above are specified by structural engineers for high-rise columns, bridges, and heavy-load structures. Do not go below M15 for any structural RCC work.
How many cement bags do I need for a 1,000 sqft roof slab?
For a 1,000 sqft slab at 4.5 inch (115mm) thickness using M20 mix with 7% wastage: wet volume ≈ 10.76 m³, dry volume ≈ 17.3 m³, cement ≈ 5.4 m³ = 7,780 kg = approximately 156 bags of 50kg. Enter your exact dimensions in the calculator for a precise figure.
What is the standard slab thickness for residential buildings in Bangladesh?
Per BNBC 2020 and common practice: residential roof slabs 4.5–5 inches (115–125mm), ground floor slabs on grade 4 inches (100mm), basement or heavy-load slabs 6 inches (150mm). Always follow your structural engineer's specification — the calculator uses your entered depth and does not assume any standard thickness.
What are the current cement, sand, and aggregate prices in Bangladesh?
As of 2024–25: Grade 43/53 cement BDT 480–550/bag (50kg), river sand BDT 1,600–2,000/m³, coarse aggregate (20mm) BDT 2,000–2,500/m³. Prices vary by brand (Lafarge, Shah, Bashundhara, Seven Rings), location, and quantity. Update the price fields in the calculator with your actual supplier quote for accurate cost.
Does this calculator include labour cost?
No — the estimate covers materials only (cement bags, sand, aggregate). Labour for mixing, placing, compacting, and curing is not included. For hand-mixed concrete in Bangladesh, add BDT 800–1,200 per m³ for labour. For ready-mix concrete (RMC), the delivered price typically includes materials and mixing — just enter your RMC price as a reference.
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