Concrete Calculator
Find the volume of concrete for a simple rectangular slab or block, with an optional allowance.
Worked example
A slab 4 m long, 3 m wide and 10 cm deep has a volume of 4 × 3 × 0.1 = 1.2 m³, which is 1,200 litres. With a 10% allowance you would plan for 1.32 m³.
How we calculated this
The volume of a rectangular slab or block is its length multiplied by its width and its depth. Each measurement is converted to metres exactly before being multiplied, so mixing units gives the same answer as using one unit. The result is shown in cubic metres, cubic feet and litres.
An allowance is added only if you type a percentage, and it is shown separately from the plain volume.
A result written as a plain number is exact. A result starting with “≈” has been rounded to 10 significant figures, because its exact decimal never ends or is too long to read comfortably. When an exact value is long, its full digits are shown underneath. The calculation itself is never rounded: only the display is.
What this result means
The result is the volume of one rectangular slab or block, in cubic metres, cubic feet and litres.
Common mistakes
- Entering the depth in the wrong unit. A depth in centimetres or inches is very different from the same number in metres or feet.
Assumptions and limitations
- It is a volume for one simple rectangular shape. It does not cover strength, reinforcement, mix, bags or weight.
- Ground that is uneven or dug too deep can use more concrete than the plain volume, so you may want to type an allowance.