What this tool does
Computes the concrete volume of a rectangular slab and the order quantity after waste. Net volume is length × width × thickness, then multiplied by the waste allowance.
How to use it
- Enter length and width in metres.
- Enter thickness in metres — 15 cm is 0.15.
- Enter the waste allowance as a percentage.
- Run it to get both net volume and order volume.
Worked example
10 m × 5 m × 0.15 m gives 7.5 m³ net, and 8.25 m³ to order with a 10% allowance.
Calculation method
Net concrete volume
length*width*depthOrder volume
length*width*depth*(1+waste/100)Frequently asked questions
- Can I enter thickness in centimetres?
- No. All three dimensions must be in metres for the result to be in m³. Entering 15 is read as 15 m and gives a figure 100× too large.
- What waste allowance should I use?
- It depends on site conditions and formwork accuracy. The 10% default is illustrative — use the figure your supplier or site lead specifies.
What this tool does not cover
It is a rectangular quantity estimate only — no structural or mix design. Slopes, stepped slabs, and reinforcement displacement are not accounted for.