How much wastage should I add for a slab?
5–10% is typical for simple slabs. Complex shapes or steep access may need more.
Slab Concrete Calculator
Calculate concrete volume for floor slabs including wastage allowance.
Slab Concrete Calculator Formula
- Slab Volume
Length × Width × Thickness - Unit Conversion
Convert dimensions to metres when ft is selected - Wastage Allowance
Base volume × (1 + Wastage ÷ 100) - Supporting Metrics
Convert m³ to ft³ for ordering
Assumptions
- The slab is treated as a uniform rectangular pour.
- Wastage covers spillage, over-excavation, and uneven sub-base.
- Reinforcement and formwork are excluded from volume.
Frequently Asked Questions
Is thickness the same as depth?
Yes. Enter the slab thickness (depth) in the same unit as length and width.
How is this different from the Concrete Volume Calculator?
This tool is slab-focused and includes wastage allowance by default in the primary result.