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🏗️ Concrete Calculator

Estimate the volume of concrete needed for slabs, columns, footings, or rectangular pads. Get results in m³ and cubic yards, plus the number of ready-mix bags required and the approximate weight of the pour.

Concrete Mix Ratios

The mix ratio (Cement : Sand : Aggregate) determines the concrete grade and its compressive strength (fck in MPa at 28 days). Higher cement content gives stronger concrete but increases cost.

Grade Mix Ratio fck (MPa) Typical Use
M101 : 3 : 610Lean concrete, backfill
M151 : 2 : 415Plain concrete slabs
M201 : 1.5 : 320RCC beams, columns, slabs
M251 : 1 : 225Heavy structures, bridges
M30+Design mix30+High-rise, industrial
'What is the difference between concrete mix ratios?', 'answer' => 'The mix ratio describes the proportion of cement : sand : coarse aggregate by volume or weight. A richer mix (more cement) like M25 (1:1:2) produces stronger concrete than a lean mix like M10 (1:3:6). The "M" grade represents the characteristic compressive strength in MPa at 28 days.'], ['question' => 'Ready-mix concrete vs. bagged concrete — which should I use?', 'answer' => 'Ready-mix (truck-delivered) concrete is cost-effective for large pours (generally above 1–2 m³) and provides consistent quality. Bagged concrete is more practical for small DIY projects, repairs, or areas with difficult access. For anything over 5 m³, ready-mix is usually recommended to save time and ensure consistency.'], ['question' => 'How much does concrete weigh?', 'answer' => 'Normal-weight (standard) concrete weighs approximately 2300–2400 kg/m³. Lightweight concrete can weigh as little as 1600 kg/m³, while heavyweight concrete (for radiation shielding) can exceed 3500 kg/m³. This calculator uses 2400 kg/m³ as the standard density.'], ['question' => 'How much should I order to allow for waste?', 'answer' => 'Always order at least 5–10% more than your calculated volume to account for spillage, over-pour, and uneven ground. This calculator automatically shows a 10% waste-allowance volume. For complex shapes or large pours, consider a 15% buffer.'], ]" />

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