The Builder’s ToolkitFree UK building calculators
Complete slab quantity planner

Concrete Slab Materials Calculator

Turn your chosen slab build-up into separate excavation, sub-base and concrete quantities. You supply the depths, density, product yield and allowance—the calculator does not invent a structural specification.

ExcavationOptional sub-baseConcreteBuying quantities

Enter your slab build-up

Use the dimensions and layer depths from your own design or specification.

m
m
mm
Geometric excavation only; no spoil bulking factor is added here.
mm
%
Applied separately to sub-base and concrete, not excavation.
mm
t/m³
Use a value appropriate to the actual material and basis you are ordering.
kg
L
Enter the product’s stated finished-concrete yield.

Read the layers as separate quantities

Concrete slab — your chosen depth
Optional sub-base — your chosen depth
Excavation / formation — your chosen dig depth
Concrete volume = area × slab depthSub-base volume = area × selected depthExcavation = area × dig depth

The calculator intentionally does not force the layers to add up to the excavation depth. If your selected sub-base and concrete layers are deeper than the excavation entered, it warns you but leaves the quantities untouched. That makes an input mistake visible instead of silently rewriting your design.

This is a quantity planner, not a slab specification

Required slab depth, sub-base construction, reinforcement, concrete specification, ground preparation and drainage depend on the project, loading, ground conditions and design. Use the depths from your drawing, specification, product system or competent professional. The calculator only converts the values you choose into quantities.

Why sub-base tonnes are optional

Volume is determined by geometry; mass depends on material density and on what the supplier’s quoted density represents. Enter a density that is appropriate to the material and ordering basis you are actually using. The result keeps volume visible so you can compare it with supplier information instead of relying on a hidden universal tonnage factor.

Bagged concrete is product-specific

If you choose bagged concrete, use the manufacturer’s finished yield for that product. The estimator rounds the allowance-adjusted requirement up to a whole number of bags and shows the mathematical bag count alongside it.

Related concrete tools

For concrete only, including circular pours, post holes or several separate pours, use the Concrete Calculator. Before placing an order, read the concrete ordering guide.