Concrete Calculator for Slabs, Bags, Volume & Cost

Calculating cubic metres of concrete is straightforward: multiply length × width × depth, all in metres. For example, a typical 100mm-thick driveway that is 6m × 9m needs: 6 × 9 × 0.1 = 5.4 m³. Always add 10% for waste, making it approximately 5.94 m³. Our concrete calculator does this maths instantly and includes waste calculations.

Our concrete bag calculator instantly converts cubic metres to bags. One cubic metre of concrete weighs approximately 2,400 kg and requires around 96 bags of 25kg concrete or 120 bags of 20kg concrete. For example, a 2 m³ project needs approximately 192 bags of 25kg concrete. The calculator shows both bag sizes simultaneously, helping you choose based on price and handling preference. It also factors in your selected waste percentage for accurate purchasing.

To calculate concrete for a slab, measure length and width in metres, and thickness in millimetres or centimetres. Convert thickness to metres (divide mm by 1,000), then multiply all three dimensions. A 3.6m × 4.8m patio with 100mm thickness needs: 3.6 × 4.8 × 0.1 = 1.73 m³. Our concrete slab calculator simplifies this process - just enter dimensions in any unit and instantly see cubic metres, bags needed, weight, and estimated cost with customisable pricing.

Our concrete calculator handles multiple shapes beyond basic slabs. For cylinders/columns: π × radius² × height. For footings: length × width × depth. For steps: (rise × run × width × number of steps). For kerbs: complex cross-sectional area × length. Each shape has its own dedicated calculator with visual preview, ensuring accurate calculations for any project type. Simply select your shape, input dimensions, and get precise concrete requirements instantly.

Converting cubic metres of concrete to bags depends on bag size. Standard conversions: 1 m³ ≈ 96 bags of 25kg concrete or 120 bags of 20kg concrete. For partial volumes, multiply accordingly. Example: 0.5 m³ needs approximately 48 bags of 25kg concrete. Our calculator automatically shows both bag sizes with exact counts, including fractional bags. This helps you decide between buying fewer heavy bags or more lighter bags based on your handling capabilities.

Concrete typically weighs approximately 2,400 kg per cubic metre. To calculate cost, multiply cubic metres by price per m³ (usually £120-£160). Our concrete cost calculator shows both weight (important for delivery planning) and cost estimation with customisable pricing. You can adjust the price per cubic metre based on local rates and instantly see total project cost, helping with accurate budgeting and contractor comparisons.

Our concrete calculator stands out with unique features: calculates 5 different shapes (slab, cylinder, steps, footing, kerb), shows instant bag requirements for all sizes, generates professional PDF reports for permits and contractors, includes customisable waste factor (5-15%), supports both metric and imperial units, and provides real-time cost estimation. Unlike basic calculators, we offer a complete solution from planning to purchasing, making it the most comprehensive concrete calculator available online.