Concrete slab
Concrete slab calculator
Estimate one rectangular slab with a uniform thickness and optional full-depth rectangular exclusions.
Concrete slab
Result
Calculate concrete for a measured slab
This slab workflow separates gross footprint from full-depth exclusions before applying thickness. Enter only non-overlapping rectangles that run through the entire slab depth.
How to use it
- Measure slab length, width and uniform thickness; add each separate full-depth exclusion once.
- Enter your waste allowance and, for whole packages, the selected product's declared mixed yield.
Formula
Net area = length × width − sum of full-depth exclusion areas. Base concrete volume = net area × thickness. Required volume = base volume × (1 + waste ÷ 100).
Example
A 5 m × 4 m slab has 20 m² gross area. One 1 m × 2 m full-depth exclusion leaves 18 m². At 0.1 m thickness and 5% waste, plan 1.89 m³. Four 0.5 m³-yield packages provide 2 m³, leaving 0.11 m³.
What the estimate uses
- Thickness is uniform; exclusions are separate, rectangular and cut through the full depth.
Limits
- The calculator cannot model slopes, thickened edges, overlapping cut-outs or partial-depth recesses.
- It does not size reinforcement, assess loads, design foundations or convert dry bag mass to volume.
Slab question
Can I subtract a shallow recess?
No. Exclusions remove concrete through the full slab thickness. A partial-depth recess needs a different volume model and must not be entered as a full exclusion.