How many cement bags per m³ for different grades?▾
M15: 4.89 bags; M20: 6.33 bags; M25: 7.26 bags; M30: 8.00 bags (all 50 kg bags per m³ of wet concrete). These are based on IS456 nominal mix proportions.
What is the dry volume factor and why is it 1.54?▾
Dry ingredients occupy 54% more volume than wet concrete because loose sand and aggregate particles have significant void space between them. When mixed with water, these voids fill and the volume reduces. So 1.54 m³ of loose dry mix produces 1 m³ of wet concrete.
How do I calculate sand and aggregate quantities for M20?▾
For 1 m³ of M20 (1:1.5:3): Dry volume = 1.54 m³. Sand = (1.5/5.5)×1.54 = 0.42 m³ ≈ 650 kg. Aggregate = (3/5.5)×1.54 = 0.84 m³ ≈ 1218 kg.
What is the difference between nominal mix and design mix?▾
Nominal mix (IS456 Table 9) uses fixed volume ratios (1:1.5:3 for M20) and is suitable for small works. Design mix (IS10262) optimises ingredients for target strength, durability, and economics — required for works over 1500 m³ or above M25.
How much concrete do I need for a 100 sq ft 4 inch slab?▾
Area = 100 ft² ≈ 9.29 m². Thickness = 4 in = 0.102 m. Volume = 9.29 × 0.102 = 0.947 m³ ≈ 1.0 m³ (after 5% wastage). Using M20: approximately 7 bags cement, 0.44 m³ sand, 0.88 m³ aggregate.
Can I use river sand and river gravel for concrete?▾
River sand (natural, well-graded) is excellent for concrete if it meets IS383 grading (Zone II preferred). River gravel should be hard and durable. Avoid flaky or elongated pieces. Wash both to remove clay and silt before use.
What size aggregate should I use for beams and columns?▾
Maximum aggregate size ≤ 1/4 of minimum member dimension and ≤ 3/4 of clear cover. For 300 mm columns with 40 mm cover, use ≤ 20 mm aggregate. For thin slabs (150 mm), use 10 or 12.5 mm aggregate.
How do I allow for wastage in concrete quantities?▾
Add 5% wastage for slabs, beams, and columns (standard formwork). Add 8–10% for footings where soil irregularities mean more concrete is placed than calculated. Pre-stressed or precast elements: 2–3%.
How do I convert m³ of concrete to bags of cement?▾
Multiply concrete volume (m³) by the bags-per-m³ for your grade: M20 × 6.33; M25 × 7.26; M30 × 8.0. For a 5 m³ M20 pour: 5 × 6.33 = 31.65 ≈ 32 bags of 50 kg cement.
What is the bulk density of sand and aggregate?▾
River sand (loose): ≈1400–1600 kg/m³. Coarse aggregate (20 mm, loose): ≈1400–1500 kg/m³. Compacted values are 8–12% higher. Always use supplier-specific bulk density for accurate weight calculations.
Should I use a vibrator for concrete placement?▾
Yes. Internal needle vibrators should be used for all structural pours (slabs ≥0.15m depth, beams, columns). Vibration eliminates air pockets and improves strength by 10–15%. Limit immersion time to 5–15 seconds and overlap by 150 mm.
What is the minimum cover to reinforcement for different elements?▾
IS456 nominal covers: Mild ≤ 20 mm; Moderate 30 mm; Severe 45 mm; Very severe 50 mm. For beam stirrups (mild exposure): 15 mm. For footings (direct soil): 75 mm. Cover affects total concrete cross-section available.
Does this calculator work for concrete blocks (CMU)?▾
No — this calculator estimates poured/site-mixed concrete volume and materials for slabs, beams, columns, and footings. It does not compute concrete masonry unit (CMU) or cinder block counts. For block-based walls, use the Brick & Block Calculator instead.
How much does a cubic yard of concrete weigh?▾
This calculator uses a normal-concrete density of 150 lb/ft³ (2,400 kg/m³ in metric mode). Since a cubic yard is 27 cubic feet, that works out to 150 × 27 = 4,050 lb (about 1.84 metric tons) per cubic yard of normal-weight concrete — the same density this calculator applies when you select "Normal" concrete type.
How many 80 lb bags of concrete are in a cubic yard?▾
That depends on which product you mean. Premixed bagged concrete (like 80 lb bags of ready-mix) yields about 0.6 cubic feet per bag once mixed, so a full cubic yard (27 cubic feet) needs roughly 45 bags. This calculator instead estimates the Portland cement component of site-mixed concrete using 94 lb cement bags (the US standard), combined separately with sand and aggregate per your chosen mix ratio — its "Cement Bags" result is a different figure from a premixed 80 lb bag count.
How many yards of concrete fit in a truck?▾
A standard ready-mix concrete truck typically carries around 10 cubic yards, though capacity varies by truck and region (commonly 8–11 cubic yards). Confirm the exact capacity with your ready-mix supplier before ordering, especially for smaller "mini mixer" trucks.