Concrete quantity estimator
Work out how much concrete you actually need
A concrete calculator that shows its working: slab and footing volumes, waste allowance, and bag estimates tied to published product yields.
Concrete quantity estimate
Measure each pour area and depth; set a count for repeated identical areas. Product yields are optional for bag counts.
- Combined plan area
- m²
- Net concrete volume
- m³
- Volume with waste
- m³
- Whole bags or packs, estimated
Supplier enquiry brief
This contains only the estimate above. Nothing is sent or saved; confirm the job specification and order terms with your supplier.
Method and limitations
Model version: 2026-09-27-v1
- Each plan area uses its own depth when entered, or the shared default. Areas must not overlap; the calculator cannot detect overlap or confirm a site drawing.
- Rectangles, right-angled triangles, full circles and circular sectors are supported. Other shapes need to be split into non-overlapping supported components.
- The entered waste allowance is a planning value, not a project specification. The Concrete Society general guide gives different overage ranges for formed and unformed elements.
- Reinforcement, formwork and deep hollows are not modelled.
- Bag yield is product-specific. No generic bag count is assumed.
- Bag counts round up to whole packs. This estimate does not calculate a price or select a structural depth or mix.
Product yields and sources
- Tarmac, Blue Circle Multi-Purpose Concrete product data sheet (December 2023; observed 2026-09-25): about 0.01 m³ per bag.
- Heidelberg Materials, 40N Concrete technical data sheet (July 2025; observed 2026-09-25): about 0.008 m³ per bag.
What brought you here?
I know the size but not the volume
Enter plan dimensions and depths in metres, centimetres or millimetres. Add supported shapes with a shared default depth or per-area overrides.
I am not sure how deep it should be
Depth directly scales volume for a fixed footprint, but it is only one dimension to confirm. Use the job specification rather than choosing by preference.
Ready-mix or bags?
The break-even between site mixing and a delivered load depends on volume, access and how fast you can place it.
What happens next
- Enter plan dimensions and depths in metres, centimetres or millimetres
- Use the depth specified for the job
- Apply a waste allowance for spillage and uneven ground
- Select a product yield if you need a bag count
- Check supplier load limits and charges before booking delivery
Three useful starting points
- Concrete calculator: volume, bags and waste allowanceCalculate concrete volume from plan dimensions, depths and repeated areas in metric units; enter a waste allowance and optional product yield.
- How deep should a concrete slab be?Why slab depth is decided by the job rather than preference, and why the same size slab can need very different volumes.
- Ready-mix concrete or mixing on site?The volume, access and timing questions that decide whether a delivered concrete load or bags mixed on site is the better route.
Decision guides
This site calculates quantities. It does not quote prices, deliver concrete, or recommend a supplier.
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