Work out how much concrete you need. This free concrete calculator finds slab or footing volume in cubic metres, yards and feet, adds a waste allowance, and estimates bags and a 1:2:4 cement/sand/aggregate mix.
Slab / footing
m
m
m
%
Enter the slab dimensions (thickness in the same units). Add a waste allowance — 5–10% is typical — for spillage and uneven ground. “How many” repeats identical pours.
Concrete needed
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Enter dimensions
Cubic metres
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Cubic yards
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Cubic feet
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Bags (≈25 kg / 60 lb)
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Mix-from-scratch estimate (1:2:4 by volume)
Volume = length × width × thickness, plus your waste allowance. Bag and mix figures are estimates — bag yields and mix ratios vary by product and project, so always check the bag and confirm with your supplier.
Use this free concrete calculator to work out how much concrete you need for a slab or footing. Enter the dimensions and get the volume in cubic metres, cubic yards and cubic feet, plus a bag estimate.
What this concrete calculator does
A concrete calculator finds the volume of concrete for a rectangular slab or footing, adds a waste allowance, and converts it to cubic metres, yards and feet — with estimates for premix bags and a from-scratch 1:2:4 mix.
A slab 5 m × 4 m × 0.1 m with 10% waste is about 2.2 m³ (2.88 cubic yards).
How much waste to add
Situation
Typical waste
Even, well-formed area
5%
Average job
5–10%
Uneven ground / spillage
10%+
Bags or ready-mix?
For small jobs, premix bags are convenient — the calculator estimates how many you’d need (yields vary by product, so check the bag). For larger pours, ordering ready-mix by the cubic metre or yard is usually cheaper and easier. The 1:2:4 breakdown helps if you’re mixing from raw cement, sand and aggregate.
How to use the concrete calculator
Choose metres or feet and enter length, width and thickness.
Set quantity and a waste allowance.
Read the volume, bag estimate and mix breakdown.
Concrete Calculator FAQ
How much concrete do I need?
Multiply length × width × thickness for the volume, then add a waste allowance. A 5 m × 4 m × 0.1 m slab with 10% waste needs about 2.2 m³ (2.88 cubic yards).
How many bags of concrete is that?
It depends on the bag, but as a rough guide a 25 kg (≈60 lb) premix bag yields around 0.011 m³, so 2.2 m³ is roughly 200 bags — which is why larger pours usually use ready-mix.
How much waste should I add?
Typically 5–10%, more on uneven ground. It covers spillage, over-excavation and slight depth variations.
What is a 1:2:4 concrete mix?
A common general-purpose ratio of 1 part cement, 2 parts sand and 4 parts aggregate by volume. The calculator estimates each, using a 1.54 dry-volume factor.
How do I convert cubic metres to cubic yards?
Multiply cubic metres by about 1.308. So 2.2 m³ is roughly 2.88 cubic yards. The calculator shows both.
Is the concrete calculator free?
Yes, this concrete calculator is completely free, needs no sign-up, and gives instant results in your browser.
