Concrete Calculator
Enter slab dimensions and a mix grade to estimate concrete volume, cement bags, sand and aggregate needed.
Slab dimensions (feet)
4 in ≈ 0.33 ft
Concrete mix grade
Cement : Sand : Aggregate ratio — 1 : 1.5 : 3
Wet volume
33 cu ft
0.934 m³
Cement bags
8
50 kg each
Sand
0.392 m³
Aggregate
0.785 m³
Includes a standard 1.54× dry-volume factor for bulking and wastage during mixing. Actual material needs vary with aggregate size, mixing method and site wastage — use this as a planning estimate, and confirm quantities with your contractor or supplier.
How to use the Concrete Calculator
- Enter the length, width and depth of your slab in feet.
- Choose a mix grade (M15, M20 or M25) based on your structural requirement.
- See the wet volume, and estimated cement bags, sand and aggregate needed.
What is a concrete calculator?
A concrete calculator estimates the volume of concrete needed for a slab, footing or similar structure, and breaks that volume down into the raw materials — cement, sand and aggregate (stone) — required to mix it, based on a standard mix ratio.
How it works
First, we work out the space your slab will fill: length × width × depth. Cement, sand and stone (aggregate) take up more room as loose, dry materials than they do once mixed and set, so we scale that number up by 54% to estimate how much raw material to buy. That total is then split between cement, sand and aggregate using the ratio for your chosen mix grade.
Formula
Wet volume = length × width × depth. Dry volume = wet volume × 1.54. Each material’s volume = dry volume × (its ratio number ÷ sum of all ratio numbers). Cement bags = cement volume × 1440 kg/m³ ÷ 50 kg per bag.
Worked example
A 10 × 10 ft slab, 4 inches (0.33 ft) deep, using an M20 mix (1:1.5:3), needs roughly 33 cubic feet of wet concrete, about 8 cement bags, plus proportional sand and aggregate.
Understanding your result
- Wet volume is the actual space your finished, set concrete will occupy.
- Cement bags assumes standard 50 kg bags at typical cement density.
- Sand and aggregate are shown in cubic metres, ready to relay to your supplier.
Which mix grade should I choose?
- M15 — a leaner mix, fine for non-load-bearing work like flooring base or footpaths.
- M20 — the most common choice for house slabs, beams and columns.
- M25 — a stronger mix for heavier structural work.
Common uses
This calculator helps homeowners and site supervisors budget material quantities for a slab, footing or driveway pour before placing an order with a supplier, and compare material cost across different mix grades.
Important notes & limitations
This is a planning-level estimate using standard ratios and a fixed cement density. Real-world material needs vary with aggregate size, moisture content and site conditions — always confirm final quantities with a structural engineer or contractor for load-bearing work.
Frequently asked questions
What is a concrete calculator used for?
It's used to estimate how much concrete — and how many bags of cement, plus sand and aggregate — you'll need for a slab, footing or similar pour before ordering materials.
Why is the dry volume more than the wet volume?
Dry materials like sand and aggregate have air gaps between particles before mixing, so they take up roughly 54% more volume than the final compacted wet concrete — hence the 1.54× factor.
Which mix grade should I use?
This depends on the structural requirement of your project. For load-bearing structural work, consult a structural engineer rather than relying solely on this calculator.
How many kg is one bag of cement?
This calculator assumes the standard 50 kg cement bag used across India.
Does this calculator account for reinforcement (steel)?
No, this estimates concrete materials only — cement, sand and aggregate. Steel reinforcement quantities need a separate calculation based on your structural design.
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