Concrete volume calculator

What is a concrete volume calculator?

A concrete volume calculator works out how much concrete a rectangular slab needs based on its three dimensions: length, width, and thickness. Whether you are pouring a patio, a garage floor, a driveway, a shed base, or a footing, knowing the volume up front lets you order the correct amount of ready-mix concrete and avoid both costly over-ordering and the headache of running short mid-pour.

How does the calculator work?

Enter the length, width, and thickness of the slab, each in whatever unit is convenient (centimeters, meters, inches, feet, or yards). The calculator converts everything to a common base, multiplies the three dimensions together, and returns the volume in your chosen unit, such as cubic meters or cubic yards. Because concrete is usually sold by the cubic meter or cubic yard, the result maps directly onto what you will order from the supplier.

Measure the area you intend to fill rather than the finished surface, and use the compacted thickness of the slab. For an even pour the thickness should be consistent across the whole footprint.

Formula

For a rectangular slab with length $L$, width $W$, and thickness $t$, the volume is simply the product of the three dimensions:

All three measurements must share the same length unit before multiplying; the calculator handles that conversion for you, so you can mix units freely between fields.

Worked examples

Example 1: a patio slab

A patio measures 5 m long and 4 m wide, poured to a thickness of 0.1 m (10 cm):

You would order about 2 cubic meters of concrete for this slab.

Example 2: a thicker base

A heavier-duty base measures 10 m long and 2 m wide at a thickness of 0.2 m (20 cm):

That pour needs roughly 4 cubic meters of concrete.

Practical notes

• Add a waste allowance: ordering 5–10% extra covers spillage, uneven subgrade, and slight over-excavation so you are not left short.
• Concrete is dense and heavy, weighing roughly 2,400 kg per cubic meter, so confirm that access and any formwork can handle the load.
• For non-rectangular pours, split the area into rectangles, calculate each separately, and add the volumes together.
• A full truck typically delivers several cubic meters at once; for small jobs ask your supplier about minimum loads or part-load charges.