Concrete Calculator

Calculate number of concrete bags needed.

Explanation

Successful masonry work starts with accurate volume calculations. This concrete calculator helps you determine the number of bags of cement or ready-mix concrete needed for your slab, foundation, or post. ### Basic Formula Volume is calculated by: **Length × Width × Thickness**. The result is in cubic meters (m³). - For a 10m² slab with 10cm thickness: 10 × 0.1 = 1 m³. ### Density and Mix - Concrete weighs about **2400 kg per m³** (approx 150 lb/ft³). - For 1 m³ of concrete, you need about 350kg of cement (for a standard mix) and about 1800-2000kg of sand/gravel mix. - If using ready-mix bags (often 25kg, 30kg, or 60lb, 80lb), divide the total mass needed by the bag weight. ### Safety Margin Always plan for **5% to 10% extra** to compensate for spills, compaction, and ground irregularities.

Examples

For a slab 4m x 3m x 12cm: Volume = 1.44 m³. Weight needed ≈ 3450 kg.
Number of 30kg bags needed: approx 115 bags (for ready-mix).

FAQ

Which mix to choose?

For a patio or walkway, standard mix is fine. For a driveway (heavy load), use a stronger mix.

How long to dry?

Concrete sets in a few hours but reaches its 'standard' strength after 28 days (curing).

Disclaimer

Always verify calculations with an architect or engineer before starting work.