Concrete Volume Calculator
Calculate cubic metres of concrete for any shape — rectangular slabs, round columns, beams, steps or any custom pour. Get volume, premix bag count and cost estimate instantly. Works in metric and imperial.
🔨 Concrete Volume Calculator
📐 How It Works
Each shape has a different volume formula. Rectangular pours (slabs, footings, beams) use L×W×D. Round columns and piers use π×r²×h. Steps are calculated as a series of rectangular prisms stacked on top of each other — each step adds one more riser height of volume.
📋 Worked Example
4 concrete steps, 1.2m wide, 280mm tread, 175mm riser: Step 1 = 1.2×0.28×0.175 = 0.0588 m³. Step 2 = 1.2×0.28×0.35 = 0.1176 m³. Step 3 = 0.1764, Step 4 = 0.2352. Total = 0.588 m³. With 15% waste = 0.676 m³.
❓ Frequently Asked Questions
Break the shape into rectangles and calculate each section separately, then add the volumes together. For L-shaped slabs, triangular areas or odd shapes, divide into the simplest rectangular sections you can. Alternatively, measure the total volume of earth displaced by the pour.
One 20kg bag of premix concrete yields approximately 0.009–0.010 m³ (9–10 litres). So 1 m³ requires approximately 100–110 × 20kg bags. At 25kg bags: approximately 80–85 bags per m³. Premix bags are only economical for very small pours under 0.3 m³.
Ready-mix is more economical and gives better quality for pours over 0.5 m³. For a 1 m³ slab, bagged concrete costs 3–4 times more than ready-mix per m³. Order ready-mix for anything larger than a small post footing.
Slump measures concrete workability. 80mm slump: stiff mix for footings. 100mm: standard mix for slabs. 120mm: more workable for pours with dense rebar. Never add extra water to increase slump on site — it reduces strength. If you need more workability, ask for a plasticiser (superplasticiser) to be added at the batch plant.