Concrete slab materials calculator

Estimate outputs: Excavation volume, Compacted base, Concrete for post holes, Length with allowance. Adjust Length, Width, Slab thickness to match your project.

Inputs and units

Use the units shown beside each field. Replace the sample values with your measurements and the figures on the selected product packaging.

Parameter	Example input
Length	10 m
Width	8 m
Slab thickness	15 cm
Compacted base depth	20 cm
Rebar grid spacing	20 cm
Waste allowance	7 %

Formula and assumptions

Excavation volume
Length × Width × (Slab thickness + Compacted base depth) / 100

Compacted base
Length × Width × Compacted base depth / 100 × (1 + Waste allowance / 100)

Concrete for post holes
Length × Width × Slab thickness / 100 × (1 + Waste allowance / 100)

Length with allowance
((ceil(Width / (Rebar grid spacing / 100)) + 1) × Length + (ceil(Length / (Rebar grid spacing / 100)) + 1) × Width) × (1 + Waste allowance / 100)

ceil = round up; floor = round down; max = the greater value. Trigonometric angles are converted from degrees to radians.

Allowance is applied before rounding to whole packages. Whole units are rounded up; displayed decimals are rounded only for readability.

Geometry and material quantities do not determine load capacity or reinforcement design. Use dimensions specified in the project.

Worked example

Sample values are examples, not product specifications. Run the calculation again with your own measurements.

Result	Calculation
Excavation volume	28 m³
Compacted base	17.12 m³
Concrete for post holes	12.84 m³
Length with allowance	875.26 m

Related calculators

Related tools use separate measurements. Check their inputs before transferring quantities.