Concrete is a mix of cement, sand, aggregate (coarse stone), and water in fixed proportions. The calculator gives you both the wet volume needed and the breakdown of dry materials by weight and bags — covering all common Indian grades (M10, M15, M20, M25).
What is Concrete?
Concrete is the most-used building material in the world. It's poured in liquid form, then cures into a stone-hard mass. The strength depends entirely on the ratio of cement, sand, and aggregate. Indian Standard codes specify standard mixes by 'grade': M20 means 20 N/mm² compressive strength after 28 days of curing.
M10 (1:3:6) is the leanest mix, used for non-structural beddings under foundations. M15 (1:2:4) suits light slabs. M20 (1:1.5:3) is the workhorse of residential construction — used for slabs, beams, columns, and lintels in most Indian homes. M25 (1:1:2) is for high-load areas like multi-storey RCC.
The trickiest concept is dry volume. When you mix cement, sand, and aggregate dry, the particles have voids (empty space) between them. Adding water fills the voids and the mass shrinks. To get 1 m³ of finished wet concrete, you need ~1.54 m³ of dry materials. The calculator handles this automatically.
Volume × dry-factor, split by mix ratio
- L, W, D
- Length × Width × Depth—physical dimensions of the structure (in metres)
- Mix ratio
- Cement:Sand:Aggregate—1:1.5:3 for M20, 1:2:4 for M15, etc.
- 1.54
- Dry volume factor—compensates for voids and bulkage
How to use this calculator
Pick a shape, enter dimensions, choose the grade, set wastage. The calculator handles all material conversions.
Pick the structure shape
Slab/foundation (rectangular), column (square), or circular pillar. Determines the volume formula.
Enter dimensions
All in metres. For columns, length and width are equal. For circular: enter the diameter as 'length'.
Choose concrete grade
M20 for residential, M15 for light slabs, M25 for high-load. The grade decides the cement:sand:aggregate ratio.
Set wastage allowance
5% standard for clean projects, up to 10% for rough sites or first-time contractors.
When to use this calculator
House foundation slab
Plot 30 × 40 ft. Foundation slab 0.2 m thick. Calculator returns m³ + cement bags needed for the order.
RCC roof slab
Most common Indian residential application. M20 grade, 0.12-0.15 m thickness. Saves trips to the supplier by ordering exact amount.
Boundary wall footings
Series of small footings — calculator works for each, then you sum the totals.
Pillar/column casting
Set shape to column, enter side and height. Useful for pergolas, garden walls, gate posts.
Civil estimator's quick check
Compare contractor estimates against the calculator before approving material orders.
Common mistakes to avoid
Using wet volume directly to order cement
Always multiply by 1.54 to get dry volume first. Otherwise you'll be short by ~35%.
Mixing grades within a single pour
Stick to one grade per pour. Mixing M15 and M20 in the same slab creates uneven strength.
Skipping wastage allowance
Even careful sites lose 5-8% to spillage. Always include wastage in the calculation.
Glossary
- Mix ratio
- Proportion of cement : sand : aggregate by volume. M20 = 1:1.5:3.
- Wet volume
- Volume of finished, water-mixed concrete. The 'in-place' volume.
- Dry volume
- Volume of the dry material mix before water is added. 1.54× the wet volume.
- Compressive strength
- Strength rating after 28 days of curing. M20 = 20 N/mm². Higher = stronger and costlier.
- RCC
- Reinforced Cement Concrete — concrete with embedded steel rebar. Standard for slabs and beams.
Frequently asked questions
What grade of concrete should I use?
Why multiply wet volume by 1.54?
How many cement bags in 1 cubic metre of M20?
References
- IS 456:2000 — Code of Practice for Plain and Reinforced Concrete— Bureau of Indian Standards