PreConstruct AIA concrete takeoff comes down to three measurements for every element — the volume of concrete, the area of form that touches it, and the reinforcing inside it — plus the items around them: base, vapour barrier, finishing, curing, dampproofing and pumping. Here is how estimators take off each one.
Volume
Volume is length × width × depth. In metric, metres × metres × metres gives cubic metres; in imperial, cubic feet divided by 27 gives cubic yards. Ready-mix is ordered in whole or half units, and every estimator adds a waste allowance that depends on the element — a slab loses more than a wall held inside its forms.
Footings
Strip footings are linear: measure their length on the foundation plan and take the width and depth from the details or the footing schedule. Pad footings are counted, each with its length, width and depth. Structural schedules list them by mark — for example F1 at 1200 × 1200 × 300 with 15M @ 300 E.W., or WF1 at 600 × 250 with three 15M bars continuous.
For Part 9 houses the Ontario Building Code sets minimum strip footing widths to check against:
| Floors supported | Exterior walls | Interior walls | Column footing area |
|---|---|---|---|
| 1 | 250 mm | 200 mm | 0.40 m² |
| 2 | 350 mm | 350 mm | 0.75 m² |
| 3 | 450 mm | 500 mm | 1.0 m² |
These widths double on gravel, sand or silt with a high water table. The current code edition governs — check it.
Foundation walls
Take the whole perimeter, jogs included, and the height from the sections — heights often change around a building. Volume is length × height less window and door openings × thickness. Forms are the contact area on each face, plus the bulkheads at the ends. In Ontario, add the scope that comes with the wall: waterproofing membrane or dampproofing, weeping tile and clean stone, parging above grade and insulation, and remember that ICF walls are bought by the block rather than formed.
Slabs
Slab volume is area × thickness. Add granular base by its depth, vapour barrier by the area with laps, mesh sheets or rebar, edge forms around the perimeter, finishing by the area, saw-cut or control joints, and curing. Ontario Part 9 sets a minimum compressive strength of 20 MPa for interior floors and 32 MPa for garage floors and exterior flatwork, with garage floors and exterior steps air-entrained.
Rebar
Rebar is taken off by bar size and length — including laps and bends — and converted to mass. A callout like 15M @ 400 E.W. is 15M bars at 400 mm centres each way; (3) 15M CONT. is three continuous bars. Canadian bars by nominal mass:
| Bar | Diameter | kg per metre |
|---|---|---|
| 10M | 11.3 mm | 0.785 |
| 15M | 16.0 mm | 1.570 |
| 20M | 19.5 mm | 2.355 |
| 25M | 25.2 mm | 3.925 |
| 30M | 29.9 mm | 5.495 |
| 35M | 35.7 mm | 7.850 |
Forms
Formwork is always measured as the area of form in contact with the concrete: both faces of a wall, both sides of a footing, the edge of a slab, the sides and soffit of a beam. Openings in walls need their own forms and extra finishing.
What gets missed
- Reading only the architectural sheets — check the structural, mechanical and electrical drawings too.
- Wall heights that change around the building.
- Laps and bent bars in the rebar, and rebar unloading.
- Forms and finishing around openings and steps.
- Winter heat and blankets, pumping, and exterior flatwork.
Doing this in PreConstruct AI
You outline slabs, click along walls, trace footings and count pads; your concrete types turn them into volumes, forms, rebar and the rest, with the arithmetic on every line. It reads footing schedules, rebar callouts and concrete notes for you to check before you use them, and it never designs anything — sizes and reinforcing are the drawings’. See how concrete takeoff works.