Concrete calculator: volume, bags and materials
This concrete calculator finds the volume for a slab, footing, round or rectangular column or solid stairs, then turns it into what you buy: premix bags (25–50 kg or 40–80 lb), cement, sand and aggregate for a site mix, or a ready-mix order in m³ or cubic yards — with waste and cost.
Site mixes use the nominal-mix method — 1:2:4 (M15), 1:1.5:3 (M20) with an editable dry-volume factor of 1.54 — and are checked against IS 456:2000 Table 9. Tick RCC for a slab calculator with steel, shuttering area, self-weight and the full material cost. US users get cubic yards and 80 lb bag counts.
It is an estimating tool: confirm structural mixes and thicknesses with your engineer or the drawings, and check the latest IS edition.
How to use the Concrete Calculator
- Choose metric or imperial and pick what you are pouring: slab, footing, round column, rectangular column or stairs.
- Enter the dimensions (thickness in mm or inches, lengths in m or ft) and “How many” for identical pours.
- Add a waste allowance — 5–10% covers uneven sub-base, spillage and over-pour.
- Choose the material: bagged premix with the bag size, site mix with the cement : sand : aggregate ratio, or ready-mix.
- Enter the price per bag or per m³/yd³; tick RCC to add steel, shuttering and other prices. Copy or share the summary.
Concrete Calculator features
Five shapes
Slabs, strip footings, round piers, square columns and stairs, with the formula shown for each.
Three ways to buy
Premix bags by size, site-mixed cement/sand/aggregate by ratio, or a ready-mix volume for ordering.
Nominal mixes in kg
Cement bags and kg, sand and aggregate kg and water per m³, compared with the IS 456 Table 9 limits.
RCC slab extras
Steel by percentage, shuttering area, self-weight at 25 kN/m³ and a total cost.
Every unit at once
m³, ft³, cubic yards and litres, plus the weight for delivery planning.
Waste and cost
Over-pour percentage before bags are rounded up; prices in ₹, $, £, € and more.
How the concrete volume is calculated
Waste is added before rounding up to whole bags. 1 m³ = 35.31 ft³ = 1.308 yd³ = 1,000 litres.
| Shape | Formula | Example |
|---|---|---|
| Slab / footing | length × width × thickness | 4 × 3 × 0.1 m = 1.2 m³ |
| Round column | π × (d ÷ 2)² × height | 300 mm × 3 m = 0.212 m³ |
| Rectangular column | A × B × height | 230 × 300 mm × 3 m = 0.207 m³ |
| Stairs (solid) | width × riser × tread × n(n + 1) ÷ 2 | 5 steps, 170 × 280 mm, 1 m wide = 0.714 m³ |
Cement, sand and aggregate for a site mix
The wet volume is multiplied by 1.54 (some use 1.52–1.57) to get the dry volume of loose materials, then split in the ratio. For 1.2 m³ of 1:2:4: dry volume 1.848 m³; cement = 1.848 ÷ 7 = 0.264 m³ = 380 kg = 8 bags of 50 kg (1 bag = 0.0347 m³ at 1,440 kg/m³); sand 0.528 m³; aggregate 1.056 m³; water = cement × w/c ratio.
IS 456:2000 clause 9.3 allows nominal mixes only up to M20; Table 9 caps aggregate at 330 kg (M15) and 250 kg (M20) and water at 32 and 30 litres per 50 kg bag. M25 and above need a design mix to IS 10262:2019, so 1:1:2 is only a planning figure.
| Mix | Grade | Cement per m³ | Sand per m³ | Aggregate per m³ |
|---|---|---|---|---|
| 1 : 3 : 6 | M10 | 4.4 bags · 222 kg | 0.46 m³ | 0.92 m³ |
| 1 : 2 : 4 | M15 | 6.3 bags · 317 kg | 0.44 m³ · 704 kg | 0.88 m³ · 1,320 kg |
| 1 : 1.5 : 3 | M20 | 8.1 bags · 403 kg | 0.42 m³ · 672 kg | 0.84 m³ · 1,260 kg |
| 1 : 1 : 2 | “M25” | 11.1 bags · 554 kg | 0.39 m³ | 0.77 m³ |
RCC slab: steel, shuttering and weight
Steel = a percentage of the concrete volume × 7,850 kg/m³ — about 1 % for slabs (IS 456 minimum 0.12 % with high-strength bars). Shuttering is soffit plus edges. Self-weight uses 25 kN/m³ for reinforced concrete (IS 456 clause 19.2.1): a 150 mm slab weighs 3.75 kN/m². Exact steel comes from the steel quantity calculator; footing sizes from the footing size calculator.
Premix bag yields and ordering tips
- Premix yields roughly 12 L per 25 kg, 19 L per 40 kg and 24 L per 50 kg; US bags 0.30, 0.45 and 0.60 ft³ for 40, 60 and 80 lb. Ready-mix is usually cheaper above about 1 yd³ (0.75 m³).
- Ready-mix trucks are ordered in 0.5 m³ or ¼ yd³ steps; order the calculated volume plus waste and round up.
- Typical thickness: 100 mm (4 in) for paths and patios, 125–150 mm (5–6 in) for driveways and Indian RCC roof slabs in M20. For the walls on top use the brick calculator.
Concrete Calculator FAQ
How much concrete do I need for a 10 × 10 slab?
At 4 in thick a 10 × 10 ft slab is 33.3 ft³, or 1.23 cubic yards — about 56 bags of 80 lb premix. Add 5–10% for waste.
How many bags of cement are in 1 m³ of concrete?
About 6.3 bags of 50 kg for a 1:2:4 (M15) mix, 8 bags for 1:1.5:3 (M20) and 4.4 bags for 1:3:6, using the 1.54 dry-volume factor. Design mixes from a lab may differ.
How many 80 lb bags make a cubic yard?
A yard is 27 ft³ and an 80 lb bag yields 0.60 ft³, so 45 bags; 60 of 60 lb or 90 of 40 lb.
What is the 1.54 factor?
Loose materials hold air gaps that vanish when concrete is mixed and compacted, so the wet volume is multiplied by 1.52–1.57 (usually 1.54) to get the dry volume to buy.
Should I use premix or site mix?
Premix suits small jobs — steps, post holes, a few square metres. Site mix is cheaper for slabs and footings; ready-mix wins above about a cubic metre or where consistent quality matters.
Does the calculator include reinforcement?
Tick RCC for a rough steel weight from a percentage of the volume, with shuttering and self-weight. The real steel comes from the structural drawings. The volume is the gross concrete, as ordered; the steel displaces too little to matter.
How much does a concrete slab weigh?
Reinforced concrete is taken as 25 kN/m³ (IS 456), so each 100 mm of thickness adds 2.5 kN/m² — about 255 kg/m² or 52 psf.