Why adding four edge strips can overcount slab corners.
Does your thickened-edge takeoff count each corner twice?
Use the matching calculator
Use this decision sequence
- Use the full outside length and width for the continuous slab layer.
- Identify the band width and total edge depth already specified in your plan.
- Subtract the inner rectangle from the outside footprint to obtain the edge band area.
- Multiply that band by only the extra depth below the continuous slab, then apply one order allowance.
Keep the quantities distinct
| Quantity or assumption | How to use it |
|---|---|
| Four independent strips | Overlap at every corner unless corrected. |
| Outer minus inner rectangle | Counts the perimeter band once. |
| Full edge depth | Includes slab material already counted above. |
Worked comparison
For a 4 m by 3 m slab, a specified 0.2 m band covers 12 − 3.6×2.6 = 2.64 m². If the slab is 0.1 m thick and total edge depth is 0.3 m, the extra edge volume is 2.64×0.2 = 0.528 m³. Add the 1.2 m³ slab to obtain 1.728 m³ before allowance. Four unreconciled strips would overcount their corner overlaps.
Check before using the estimate
All sections must already be specified; the calculation does not determine whether an edge thickening is required.
All dimensions, product properties, prices and specifications in this example are illustrative arithmetic inputs. Use the values from your measured plan, selected product data sheet and supplier quote. This guide does not choose construction specifications or certify safety.
Calculation and scope checked 2026-10-04. Methods and scope.
Related decisions
Reconcile volume at crossing concrete wall segments
Is an intersection included in both wall segment measurements?
Check void deductions against their own concrete component
Why can a correct total void still produce an invalid takeoff?
Keep continuous strip lengths separate from station-to-station measurements
Are repeated strip segments measured over disjoint portions of the same run?