Concrete Calculator
Estimate the volume of concrete, number of cement bags, sand, and aggregate needed for a slab, footing, or column based on its dimensions and mix ratio.
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Your result
3 m³
Wet concrete volume
AI explanation
Formula
Dry volume = Length × Width × Depth × 1.54; material volumes split by mix ratio; cement bags = cement volume ÷ 0.0347 m³/bagWorked example
5m × 4m slab, 150mm thick, M20 mix
| Field | Value |
|---|---|
| Length | 5 |
| Width | 4 |
| Depth / thickness | 0.15 |
| Concrete mix | M20 (1:1.5:3) |
| Wet concrete volume | 3 |
| Cement required (50kg bags) | 24.2 |
| Sand required | 1.26 |
| Aggregate required | 2.52 |
Assumptions
- Dry volume factor of 1.54× the wet (poured) volume accounts for voids between aggregate, sand, and cement that close up during mixing — a standard site-estimation rule of thumb.
- One 50kg cement bag is assumed to occupy approximately 0.0347 m³ (based on ~1,440 kg/m³ loose bulk density).
- Does not include wastage allowance beyond the dry-volume factor, formwork, or reinforcement.
Frequently asked questions
What do M15, M20, and M25 mean?
These are concrete grade designations indicating characteristic compressive strength in N/mm² (e.g. M20 = 20 N/mm²). The number ratios (like 1:1.5:3) are cement:sand:aggregate proportions by volume.
Why is the dry volume larger than the wet volume?
Dry, unmixed materials (cement, sand, aggregate) have air gaps between particles. When mixed with water, they settle together into a denser wet volume — so you need about 54% more dry material than the final poured (wet) volume.
Should I add extra material for wastage?
Site conditions vary — many contractors add an additional 5-10% on top of these calculated quantities to account for spillage and handling losses, which is not included by default here.
This is a standard site-estimation calculation using common assumptions (dry volume factor, cement bag volume). Actual material requirements can vary based on aggregate size, moisture content, and mixing method — consult a structural engineer for load-bearing structural work.
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