Why is the dry volume larger than the concrete?

Because sand and aggregate have voids between the particles that water and cement paste fill. The mixture shrinks as it combines, so 1.54 cubic metres of dry material gives about one cubic metre of concrete.

How much wastage should I allow?

Five percent is normal for a clean slab. Awkward shapes, hand mixing or a long pump run all justify more.

Construction & Homematerials

Concrete Volume Calculator

Concrete volume for a slab, column or footing, with wastage and the ready-mix load count. The dry volume of ingredients is larger than the wet concrete, which is the factor most quantity errors come from.

Also called: concrete quantity, how much concrete do i need.

Concrete to order (m³)

3.15

3.15 m³ including 5% wastage, against a net 3 m³. That is about 0.53 truck loads at 6 m³, or 111.24 cubic feet.

Net volume (m³)

In cubic feet

111.24

In cubic yards

4.12

Ready-mix loads at 6 m³

0.53

Dry volume of ingredients (m³)

4.85

How this is calculated

Method and background

How this is calculated

Volume is the straightforward part. The number worth knowing is that dry ingredients occupy about 1.54 times the volume of the wet concrete they produce, because water fills the voids between particles, so ordering cement and aggregate against the wet volume leaves you short by more than a third. Ready-mix is delivered in fixed truck sizes, so the load count matters as much as the volume for anything above a few cubic metres.

volume = length * width * thickness * quantity, plus wastage; a column uses pi * d^2 / 4 * depth

l, w, t: Length, width and thickness (metres)
n: How many pours (count)
s: Wastage allowance (decimal)

Full derivation: Concrete quantities, and where the 1.54 comes from

Worked examples

Each of these is asserted on every build. If a change to the engine ever moved one of these answers, the build would fail before the page could print it.

a five by four slab at 150mm

Pour shape: Slab or rectangle
Length (m): 5
Width (m): 4
Thickness or depth (m): 0.15
Diameter, for a column (m): 0.3
How many: 1
Wastage allowance: 5%

Concrete to order (m³)3.15

5 * 4 * 0.15 = 3 m³, plus 5%

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a circular column

Pour shape: Circular column
Length (m): 0
Width (m): 0
Thickness or depth (m): 3
Diameter, for a column (m): 0.3
How many: 4
Wastage allowance: 5%

Concrete to order (m³)0.89

pi * 0.09 / 4 * 3 * 4, computed independently

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no wastage leaves the net volume

Pour shape: Slab or rectangle
Length (m): 5
Width (m): 4
Thickness or depth (m): 0.15
Diameter, for a column (m): 0
How many: 1
Wastage allowance: 0%

Concrete to order (m³)3

boundary: the 1.54 factor applied to exactly 3 m³

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Method and limits

What it assumes

Dimensions are finished dimensions, so formwork thickness is excluded.
The 1.54 dry-volume factor is the common site figure and ranges from 1.52 to 1.57.

What it deliberately does not model

Reinforcement displaces a small amount of concrete, which is conventionally ignored.
Complex shapes need to be broken into rectangles and summed.

Sources

Bureau of Indian Standards, IS 456 and IS 2212 (standards body)

Formula version 1.0.0 · definition 1.0.0 · United States · Report a problem with this calculator

Frequently asked questions

Why is the dry volume larger than the concrete?: Because sand and aggregate have voids between the particles that water and cement paste fill. The mixture shrinks as it combines, so 1.54 cubic metres of dry material gives about one cubic metre of concrete.
How much wastage should I allow?: Five percent is normal for a clean slab. Awkward shapes, hand mixing or a long pump run all justify more.