How to Estimate Concrete: A Complete Guide
A practical, step-by-step method for converting slab, footing, or column dimensions into an accurate concrete order — including the wastage allowances suppliers expect you to already know.
Published 10 January 2026 · Updated 2 May 2026
Concrete is sold and poured by the cubic meter (or cubic yard), so the entire ordering process comes down to one question: how much volume does your pour actually need?
Start with the plan area — length multiplied by width — of the element you're pouring. For a slab, this is straightforward. For a footing or column, measure the cross-sectional footprint instead. Multiply that area by the thickness or height to get the raw volume.
Raw volume is never the number you order. Real-world pours lose material to sub-base irregularities, formwork seepage, and over-excavation, so estimators add a wastage allowance — typically 5% for a machine-poured slab on prepared ground, rising to 10% for hand-poured or irregular work.
Once you have a final volume, round up to the supplier's minimum order increment, usually a quarter or half cubic meter, or to the nearest full truck load for large pours. Ordering short mid-pour is far more expensive than a small surplus, both in delay and in the risk of a visible cold joint where two batches meet.
For mixed or on-site batching rather than ready-mix delivery, you'll also need to convert that volume into bags of cement, sand, and aggregate using your target mix ratio — that's a separate calculation covered in the Cement Ratio Guide.