Concrete Slab Calculator
Enter slab dimensions and quantity to compute concrete volume, weight, bag count and cost for footings, slabs and small structures.
Input Data
Results
At a glance:The core of the concrete calculator is the "volume × density" model: first derive concrete volume from member size, multiply by density for weight; bags needed = weight × (1 + wastage%) ÷ bag weight rounded up; total cost = bags × price per bag. Default density 2,400 kg/m³ matches ordinary (in-situ) concrete.
Formula
Total area A = length × width × quantity
Volume V = length × width × thickness × quantity
Weight W = V × density
Bags N = ⌈ W × (1 + wastage%) ÷ bag weight ⌉
Total cost = N × price per bag
Example: 5m×3m×10cm slab → 1.5 m³, ~3,600 kg, ~76 bags at 50 kg with 5% wastage
$$A = L W n$$$$V = L W H n$$$$W = V \rho$$$$N = \left\lceil \frac{W(1+w\%)}{B} \right\rceil$$How to Use
- Enter the length, width and thickness of the member.
- Enter the quantity of identical members.
- Confirm the concrete density and bag weight.
- Set the wastage percentage.
- Enter price per bag to estimate cost (0 to skip).
- The tool outputs area, volume, weight, bags and cost.
Common concrete density reference
| Concrete type | Density (approx.) | Weight per m² of 10 cm slab |
|---|---|---|
| Ordinary concrete | 2,400 kg/m³ | 240 kg |
| Lightweight concrete | 1,800 kg/m³ | 180 kg |
| Heavy concrete | 2,600 kg/m³ | 260 kg |
Density varies with aggregate; use the supplier's value for accuracy.
Case Studies
Home slab
Re-pour a 5m × 3m, 10 cm slab in the living room.
Concrete volume = 1.5 m³, weight about 3,600 kg.
At 50 kg bags with 5% wastage, about 76 bags, orderable from a building-supply shop.
Pier footings
Pour 4 identical pier footings, each 0.8×0.8×0.5 m in the garden.
Each 0.32 m³, 4 total 1.28 m³, weight about 3,072 kg.
At 20 kg bags with wastage, about 162 bags, good for staggered delivery.
Project quote
A small contractor receives a slab quote and needs the material cost.
After entering price per bag, total cost is the material basis.
Adjust wastage to site reality, usually 5% is enough.
FAQ
How many bags in 1 m³ of concrete?
1 m³ ordinary concrete weighs about 2,400 kg. At 50 kg bags that is 48 bags (no wastage); at 20 kg bags, 120 bags.
What wastage percentage to use?
Form leakage and transfer loss during pour usually account for 5–10%. The calculator defaults to 5%, adjustable to site conditions.
Can I skip cost?
Yes. When price per bag is 0, total cost outputs 0, but you still get volume, weight and bag count.
Bagged vs ready-mix?
Small jobs suit bagged dry-mix for flexibility; large volumes are cheaper as ready-mix delivered by truck. Compare cost per m³ to decide.
Related Tools
References
Content review: Calculatorism Science Team. Results are for reference only; please refer to the relevant authorities for the official figures.