KORA concrete takeoff comes down to volumes: length × width × thickness. Mistakes rarely come from the multiplication. They come from units (inches, feet and cubic metres mixed together), from a wall length measured to the wrong face, or from formwork and rebar left out. Here's a clear method, with a complete example.
What you need before you start
- Foundation wall lengths, measured on the foundation plan, at the centre of the wall. Measured to the outside face, every corner counts some concrete twice.
- Footing dimensions (width and thickness) and wall dimensions (height and thickness), from the section or the details.
- Slab area and thickness.
- Isolated footings and columns (piers, posts), with their dimensions.
- Your concrete waste factor: often around 5%, depending on the ground and the forms.
Cubic metres or cubic yards
In Québec, concrete is ordered in cubic metres (m³). Elsewhere in North America, cubic yards (yd³) are common. The conversion:
The most common trap: multiplying feet by inches. Convert everything to the same unit before you multiply (e.g. 10" = 0.833 ft), or let a tool do it for you.
1. Strip footing
Footing formwork covers both sides:
Footing rebar is counted in continuous bars:
Laps (bar overlaps) are covered here by a percentage, often around 10%. If your drawings call for specific lap lengths, you can also count them bar by bar.
2. Foundation wall
Wall rebar has two parts:
- horizontal: length × number of rows, + laps and waste;
- vertical: (length ÷ spacing, rounded up, + 1 bar at the end of each wall) × height, + laps and waste.
Anchor bolts follow the same logic: length ÷ spacing, rounded up, + 1 per wall. Also add dampproofing (length × height) and weeping tile (length, plus a small margin).
3. Slab
The materials under and in the slab use the same area: rigid insulation, 6 mil poly and wire mesh, the last two with about 10% extra for overlaps. Measure the area inside the foundation walls, not the outside footprint.
4. Isolated footings and columns
Isolated footings (under columns or posts) don't all have the same size. The simplest way: trace each one in plan as a rectangle (an area), then multiply:
- concrete = area × thickness, + waste;
- formwork = perimeter × thickness (all 4 sides);
- rebar both ways = bars × (width + length) of each footing, which equals bars × perimeter ÷ 2.
Concrete columns work the same way, with height instead of thickness. A round column is traced as a circle: concrete is area × height and the form (cardboard tube) has the same height. Ties are counted from their spacing: (height ÷ spacing, rounded up, + 1) × column perimeter.
Worked example: a bungalow foundation
Assumptions (common values, to replace with those on your drawings):
- foundation walls: 136 lin. ft measured at the centre, in 4 walls;
- 24" × 10" footing, 2 continuous bars;
- wall 8 ft high × 8" thick, 3 rows of horizontal bars, vertical bars at 24", anchor bolts at 6 ft;
- 1,000 sq. ft slab × 4";
- 3 isolated footings 2 ft × 2 ft × 12", 4 bars each way;
- waste: 5% for concrete, 10% for steel.
Concrete
| Item | Calculation | Result |
|---|---|---|
| Footing | 136 × 2 × 0.833 = 226.7 cu. ft = 6.42 m³, × 1.05 | 6.74 m³ (8.81 yd³) |
| Wall | 136 × 8 × 0.667 = 725.3 cu. ft = 20.54 m³, × 1.05 | 21.57 m³ (28.21 yd³) |
| Slab | 1,000 × 0.333 = 333.3 cu. ft = 9.44 m³, × 1.05 | 9.91 m³ (12.96 yd³) |
| Isolated footings | 3 × 4 sq. ft × 1 = 12 cu. ft = 0.340 m³, × 1.05 | 0.36 m³ |
In total, about 38.6 m³ of concrete, in three or four separate pours. Order each pour separately and round up according to your supplier's requirements: the footing and the slab don't go in the same truck.
Formwork and rebar
| Item | Calculation | Result |
|---|---|---|
| Footing formwork | 136 × 0.833 × 2 | 226.7 sq. ft |
| Wall formwork | 136 × 8 × 2 | 2,176 sq. ft |
| Footing rebar | 136 × 2 = 272, × 1.10 | 299.2 lin. ft |
| Wall horizontal rebar | 136 × 3 = 408, × 1.10 | 448.8 lin. ft |
| Wall vertical rebar | 136 ÷ 2 = 68, + 4 walls = 72 bars × 8 = 576, × 1.10 | 633.6 lin. ft |
| Anchor bolts | 136 ÷ 6 = 22.7 → 23, + 4 walls | 27 bolts |
| Isolated footing formwork | perimeter 3 × 8 = 24 ft × 1 | 24 sq. ft |
| Isolated footing rebar | 4 × 24 ÷ 2 = 48, × 1.10 | 52.8 lin. ft |
Key points:
- Add up before rounding. The 136 lin. ft is calculated as one total; only the "+ 1 per wall" depends on the number of walls.
- Concrete waste doesn't apply to formwork. Formwork is calculated on the actual dimensions; its own waste (damaged lumber, reuse) depends on your forming system.
- Rebar in linear feet is then converted into stock-length bars (e.g. 20 ft) according to your supplier.
Common mistakes
- Measuring walls to the outside face: every corner counts the wall thickness twice.
- Missing garage walls, porch stem walls or fireplace footings, often drawn on another sheet.
- Multiplying inches by feet without converting.
- Counting waste twice: once in the volume, again by rounding every pour up generously.
- Forgetting garage or porch slabs, which often have a different thickness.
In KOR
KOR includes starter templates for foundations, using the rules in this article, all editable: "Footing and foundation wall" (trace the wall length at the centre; footing and wall concrete in m³, formwork, rebar, anchor bolts, dampproofing, weeping tile), "Concrete slab" (trace the area), "Isolated footings (piers, columns)" and "Concrete columns" (each traced as a rectangle, or a circle for a round column, with its own dimensions). Units are converted automatically, the math runs on each item's total, and the quantities go straight into the estimate.
Summary
- Measure foundation walls at the centre, and convert every dimension to the same unit.
- Concrete = length × width (or height) × thickness, + waste; slab = area × thickness, + waste.
- Formwork = length × thickness or height × 2 sides; isolated footings and columns: perimeter × thickness or height.
- Rebar: continuous bars × length, vertical bars from the spacing, + laps.
- Order concrete pour by pour.