Concrete Volume Calculator

How the Concrete Volume Calculator works

The concrete volume calculator determines the volume of fresh concrete required for slabs, columns, beams, footings, and retaining walls. Enter element dimensions to get volume in cubic metres, then apply the dry volume factor of 1.54 to compute exact quantities of cement (bags), sand (m³), and coarse aggregate (m³) for your chosen mix design — ready for procurement and cost estimation.

Dry volume factor of 1.54

When cement, sand, and aggregate are mixed dry, the total volume exceeds the wet concrete volume by about 54% because dry particles pack loosely. To produce 1 m³ of compacted wet concrete, you need approximately 1.54 m³ of dry ingredients. This factor is the source of the seemingly counter-intuitive material quantities in concrete calculations and is applied automatically by the calculator.

Element-specific calculations

Slab volume = length × width × thickness. Column volume = cross-section area × height (add haunches separately). Beam volume = width × depth × span. Footing volume combines the base pad and pedestal. For circular elements, the cross-section area uses πr². The calculator handles all these geometry variations and lets you add multiple elements to get a total project concrete volume for a single pour.

Mix design and material quantities

For M20 grade (1:1.5:3 nominal mix), each cubic metre of concrete requires approximately 8 bags of 50 kg cement, 0.42 m³ of fine aggregate (sand), and 0.83 m³ of coarse aggregate (20 mm jelly). For M25 (1:1:2) the cement content rises to around 10 bags per cubic metre. The calculator supports M10 through M30 mix designs and scales all material quantities to your entered volume.

Ready-mix vs site-mixed concrete

For volumes above 5–10 m³, ready-mix concrete (RMC) from a batching plant is usually more economical than site mixing. The calculator's volume output is directly usable for ordering RMC in cubic metres. For smaller pours, the bag counts guide manual mixing on site. Knowing the exact volume prevents costly over-ordering of RMC trucks, since minimum delivery charges apply to partial loads.

Frequently asked questions

How is concrete volume calculated for a slab?

Slab volume = Length × Width × Thickness. For example, a 5 m × 4 m slab with 150 mm thickness gives 5 × 4 × 0.15 = 3 m³ of concrete. Always convert thickness to metres before calculating. Add a 5–10% wastage factor to the result to account for spillage and uneven formwork.

How many bags of cement per m³ for M20 concrete?

For M20 concrete using a nominal 1:1.5:3 mix ratio, approximately 8 bags of 50 kg cement are required per cubic metre of finished concrete. This works out to about 400 kg of cement, 600 kg of sand, and 1,200 kg of aggregate per cubic metre.

What wastage factor should I use?

For regular slab and column work with standard formwork, use a 5% wastage factor to account for spillage and minor overpouring. For work with complex formwork shapes, remote pours, or difficult site access, increase the wastage factor to 8–10%. Always order slightly more than calculated to avoid delays from a shortage.