Concrete Slab Calculator
Calculate the concrete volume and cement/sand/aggregate quantities needed for a flat slab.
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Your result
3
Wet concrete volume
AI explanation
Formula
Wet volume = length × width × thickness; dry volume = wet volume × 1.05 (or your wastage %) × 1.54; split by mix ratio partsWorked example
5m × 4m slab, 150mm thick, M20 mix, 5% wastage
| Field | Value |
|---|---|
| Slab length (m) | 5 |
| Slab width (m) | 4 |
| Slab thickness (m) | 0.15 |
| Concrete mix | M20 (1:1.5:3) |
| Wastage allowance (%) | 5 |
| Wet concrete volume | 3 |
| Cement bags (50kg) | 25.4 |
| Sand volume | 1.323 |
| Aggregate volume | 2.646 |
Assumptions
- Dry volume = wet volume × 1.54, a standard site-estimation factor accounting for the voids between aggregate/sand/cement particles that close up during mixing.
- One cement bag is 50kg (~0.0347 m³).
- Nominal mix ratios (M15/M20/M25) are used for simple residential estimation — critical or large structural pours should use a design mix per IS 456, verified by a structural engineer.
Frequently asked questions
How thick should a residential concrete slab be?
100-150mm (4-6 inches) is typical for a residential floor slab; driveways and heavier-load slabs are often 150mm or more. Check your structural drawing for the exact specification.
Which mix ratio should I choose?
M20 is a common general-purpose choice for residential slabs in India. M15 is leaner (used for less critical work like flooring beds), and M25 is richer (used for higher strength requirements) — follow your structural engineer's specification.
Why is the dry volume larger than the wet volume?
Dry, loose cement/sand/aggregate have air gaps between particles that close up once mixed with water — so you need about 1.54 times the finished (wet) volume in dry materials.