Free calculator

Concrete calculator

Turn length, width and thickness into volume, mix weight, complete bags and approximate cost.

✓ Volume in m³✓ Safety margin included✓ Bags and cost

Your inputs

Dimensions, mix and packaging

Updates instantly

LearnMaterial calculatorsSee related calculators →

Indicative diagram of this calculator inputs — Volume = length × width × depth; first convert all measurements to metres.

How we calculate concrete

We convert thickness from centimetres to metres, multiply by length and width, add the margin and then use density to estimate kilograms and bags.

length × width × (thickness ÷ 100) × (1 + margin)

Density is an estimate

Density and yield vary by product and water content. The manufacturer data sheet takes priority over any generic value.

Do not ignore logistics

More than one hundred bags means a lot of weight, transport, storage and mixing time. Cost is not the only factor.

How to use the concrete estimate without under-ordering

The geometric volume is only the starting point. Real jobs can need extra material because the base is uneven, edges are irregular or some mix is lost during transport, mixing and placement. The margin field is there to account for that uncertainty.

Thickness has the biggest effect

A small change in average thickness can add a large amount of concrete over a wide area. Measure at several points, especially on an existing base that is not perfectly level, and use the finished thickness required by the job rather than guessing from one edge.

Bags and ready-mix are different decisions

For small repairs, bags can be practical. For larger volumes, the total bag count can become heavy, slow to mix and difficult to place consistently. Use the result to compare logistics as well as purchase price.

For a worked planning method, read how to calculate concrete for a slab. For non-structural masonry and repair work, the mortar calculator may be more appropriate.

Editorial review: 11 Oct 2026. Structural concrete design and load-bearing work require suitable technical specification.