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Concrete slab calculator
Enter the slab size, thickness and strength, and get the concrete volume, reinforcing mesh, chairs, membrane and edge formwork, plus the hours to form, pour and finish it.
AnySlab
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Open AnyBuild freeHow the slab takeoff is worked out
Concrete is the line you cannot fix after the truck leaves, so the volume is deliberately rounded up:
- Volume is area x thickness, plus 5% for the base not being perfectly level and for what stays in the barrow, then rounded up to the nearest 0.2 m³ (or 0.5 cubic yard) because that is how it is ordered.
- Mesh is counted by effective sheet coverage after lap, not raw area, so the sheet count already allows for the 225 mm laps.
- Membrane and bar chairs scale off the slab area and mesh count.
- Edge formwork is taken from the perimeter, with a little extra for stakes and joins.
- Labour is concreter hours for forming, pouring, screeding and finishing, plus a labourer allowance, with a base allowance so a small slab is not under-costed.
Things worth checking before you order
- Slab thickness and reinforcement should come from the site classification and the footing design. AS 2870 (AU) or ACI 332 / IRC R506 (US) set the requirements, and reactive clay sites in particular need engineering.
- Order concrete a little early in the day and have more hands than you think you need. Running short mid-pour is far more expensive than a small over-order.
- If the truck cannot reach the slab, add the pump. It changes the price materially and is a checkbox here.
- Curing matters as much as the mix. Plan how you will keep it damp before you pour, especially in summer.
Common questions
How much concrete do I need for a 6 x 4 m slab?
At 100 mm thick that is 2.4 m³ of net volume, so about 2.6 m³ ordered once waste is allowed. The calculator rounds to how concrete is actually ordered and adds the mesh, membrane and formwork with it.
How do I convert a slab to cubic yards?
One cubic yard is 27 cubic feet, so multiply the area in square feet by the thickness in feet and divide by 27. Switch the calculator to the United States setting and it works in cubic yards and psi throughout.
What concrete strength should I use for a shed or garage slab?
25 MPa suits most shed slabs and paths, with 32 MPa where loads are heavier; the US equivalents are 3000 and 4000 psi. Check what your local requirements and the slab design call for.
Does the calculator include the mesh laps?
Yes. The sheet count is based on effective coverage after lapping, so you are not ordering short.
These figures are indicative and use sample regional trade prices, so treat them as a starting point for a quote rather than a final price. Quantities follow common practice and standard allowances; spans, footings, fixings and compliance for your specific job should be confirmed against the current standards and, where required, an engineer.
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