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Concrete Calculator

Your project

Project type
How do you want to measure?
ft
ft
in
in

Compacted gravel under the slab. Enter 0 for none.

%

5–10% is typical for slabs; footings in rough trenches often need more.

per yd³

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Concrete needed, including waste

3.26 cubic yards

Base volume
2.96 yd³
Waste allowance (10%)
+ 0.30 yd³
Total required
3.26 yd³ (88 ft³)
Recommended orderRounded up for ready-mix delivery.
3.50 yd³
Premixed 60 lb (27 kg) bags≈ 0.45 ft³ (13 L) per bag
196
Premixed 80 lb (36 kg) bags≈ 0.60 ft³ (17 L) per bag
147
Slab areaArea for reinforcing mesh, vapour barrier and forms.
240 ft²
Gravel base neededAbout 4.39 short tons of crushed stone, incl. waste.
3.26 yd³ (88 ft³)

Inputs

  • Project type: Slab
  • How do you want to measure?: Length × width
  • Length: 20 ft
  • Width: 12 ft
  • Thickness: 4 in
  • Gravel base depth: 4 in
  • Waste / overage: 10 %
  • • 1 cubic yard = 27 cubic feet = 0.7646 m³. Your total is 3.26 yd³.
  • • Above roughly 1–2 cubic yards, ready-mix delivery is usually easier than mixing bags. Ask your supplier about minimum loads.
  • • The gravel base figure assumes crushed stone at about 2,700 lb/yd³. For other densities or depths, use the gravel calculator.
  • • Most slabs also include steel mesh or rebar. Check your local code and your plans for the right type and spacing, and size the bars with the rebar calculator.

Results are estimates for planning only. Supplier specifications, product yields, site conditions and local codes vary. Confirm quantities with your supplier or a qualified professional before you buy or build.

Concrete Calculator by BuildKit