How to calculate concrete volume without running short
Ordering premix concrete requires exact measurements, because running short by even a quarter of a cubic metre can ruin a pour and require an emergency truck delivery with a small-load surcharge. Always measure the length, width, and actual dug depth in metres, multiplying all three to find the cubic metre volume.
Real ground is never perfectly flat or level. Formwork can bow under the heavy wet hydraulic pressure of wet concrete, and uneven sub-base trenches often absorb extra material. A golden rule among Australian concreters is to always add an extra 10% for paths and slabs, or up to 15% for rough uneven fence post footings.
Before the agitator truck arrives, have all formwork braced and pegged securely, moisture barrier plastic taped, and steel mesh placed on bar chairs. Never let reinforcement mesh sit on the bare ground, or it will provide zero tensile strength to your cured slab.
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