Concrete takeoffs live or die on one core calculation: volume. For a footing or slab, that's length × width × depth, converted to cubic yards (divide cubic feet by 27) — straightforward for a simple rectangular foundation, more involved once step footings, thickened edges, or grade beams enter the picture, each of which needs its own volume calculated separately and summed.
Rebar
Rebar is estimated by linear footage of each bar size specified, based on spacing called out in the structural plans (commonly on 12" or 16" centers for footings), plus overlap/lap length at splices — typically 40 times the bar diameter, though this should always be confirmed against the project's structural specs rather than assumed as a universal standard.
Formwork
Formwork is measured by the linear footage of footing/wall perimeter multiplied by height, accounting for corners and any step-downs in grade — and unlike the concrete volume itself, formwork is frequently reused across a job, so the takeoff should reflect actual lumber/panel needs rather than a one-time-use assumption.
The waste factor to watch
Concrete ordering typically includes 5–10% extra to account for spillage, over-excavation, and irregular subgrade — under-ordering concrete mid-pour is one of the costliest mistakes on a foundation job, since a stalled pour can compromise the integrity of the finished element.