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Concrete Calculator
Estimate concrete for a rectangular slab or footing using metric dimensions. Review base and order volume, wet weight, ready-mix loads, bag estimates, scenario depths, and export a professional PDF.
Base concrete volume0 m3
Recommended order volume0 m3
Approximate wet weight0 kg
Approximate 25 kg bags0
Depth sensitivity
Volume at alternative slab depths
Order volume by thicknessIncludes current waste allowance
| Thickness | Base volume | Order volume | Wet weight | 20 kg bags | 25 kg bags |
|---|
Slab view
Concrete slab footprint, depth, waste, and order volume
Footprint, depth, base volume, and ordering margin are shown as a buildable slab estimate.
Concrete slab footprint, depth, waste, and order volume
Footprint
Depth
Base volume0
Order volume0
Weight0
Bag count0
How to use Concrete Calculator
- Enter slab length, width, depth, and waste allowance using consistent units.
- Review base volume separately from order volume so waste and placement margin are visible.
- Use the slab cross-section visual and scenario table to judge whether a change in depth has a meaningful order impact.
Calculator guide
Understanding Concrete Calculator
Concrete ordering starts with geometric volume and then adds an allowance for grade variation, spillage, and placement loss. Bag estimates depend on product yield, not bag weight alone.
Calculation method
How the calculation works
Rectangular concrete volume = length x width x thickness, converted to cubic meters and increased by the waste allowance. Convert millimeter thickness to meters, multiply dimensions for cubic meters, apply waste, then convert using approximate density and bag-yield assumptions.
Concrete volume method
Before ordering concrete
Worked situations
Practical examples
- Estimate a 4 m by 6 m slab at 100 mm thickness.
- Add a practical waste allowance for uneven grade and handling loss.
- Compare 20 kg, 25 kg, and 40 kg premix bag estimates.
Better inputs
Useful tips
- Measure several depths when the subgrade is uneven.
- Confirm truck minimums and bag yields with the supplier.
- Plan access, labor, and placement before concrete arrives.
Before relying on the result
Limitations and common mistakes
- Only rectangular slabs or footings are modeled.
- Density and premix yield vary by product and mix design.
- Structural sizing and reinforcement require qualified design.
Reference
Key terms
- Volume
- Three-dimensional quantity expressed here in cubic meters.
- Thickness
- Slab depth converted from millimeters to meters.
- Yield
- Wet concrete volume produced by one bag.
- Waste
- Extra order volume for site variation and loss.
Important note
Calculated from the entered measurements and stated coverage or quantity rules. Confirm field dimensions, waste, product requirements, structural conditions, and local codes before purchasing or building.
Frequently asked questions
How is slab volume calculated?
Multiply length by width by thickness after converting thickness to meters.
Why add waste?
Actual forms and subgrades are imperfect, and placement can involve loss.
Are bag estimates exact?
No. Check the manufacturer's stated yield for the specific product.
Does this design slab thickness?
No. Structural dimensions should come from applicable plans or qualified advice.