How concrete volume is calculated
Concrete volume is length × width × depth of the pour. A slab 5 m long, 4 m wide and 150 mm (0.15 m) deep holds 3 m³ of concrete. This calculator works out that volume in cubic metres and cubic feet and can then estimate the cement, sand and aggregate needed to mix it on site.
It's meant for rectangular pours: slabs, footings, pads, driveways and paths. Each of the three dimensions has its own unit selector, so "10 ft by 10 ft by 4 in" works without converting by hand.
The formulas
Volume = Length × Width × Depth (all converted to metres)
If you pick a mix ratio, the material estimate runs in four steps:
- Dry volume = wet volume × 1.54. Dry ingredients contain voids that disappear when water is added and the concrete is compacted.
- Add wastage, 5% by default and editable from 0 to 50%. Wastage applies to the materials only; the volume shown is the net volume.
- Split by the mix ratio. For 1:2:4 there are 7 parts, so cement is 1/7 of the dry volume, sand 2/7 and aggregate 4/7.
- Cement bags = cement volume × 1,440 kg/m³ ÷ 50 kg. The calculator assumes a cement bulk density of 1,440 kg/m³ and 50 kg bags.
Worked example
A 5 m × 4 m slab, 0.15 m deep, in 1:2:4 with 5% wastage:
- Volume: 5 × 4 × 0.15 = 3.000 m³ (105.944 ft³).
- Dry volume: 3 × 1.54 = 4.62 m³.
- With wastage: 4.62 × 1.05 = 4.851 m³.
- Cement: 4.851 ÷ 7 = 0.693 m³, and 0.693 × 1,440 ÷ 50 = 19.96 bags.
- Sand: 4.851 × 2/7 = 1.386 m³. Aggregate: 4.851 × 4/7 = 2.772 m³.
In imperial units, a 10 ft × 10 ft patio 4 in thick comes to 33.333 ft³ (0.944 m³), which is about 1.23 cubic yards.
Materials per cubic metre by mix
These are the calculator's own outputs for 1 m³ of finished concrete with wastage set to 0:
| Mix (cement:sand:aggregate) | Calculator label | Cement (50 kg bags) | Sand (m³) | Aggregate (m³) |
|---|---|---|---|---|
| 1:1.5:3 | Higher strength | 8.06 | 0.420 | 0.840 |
| 1:2:4 | General use | 6.34 | 0.440 | 0.880 |
| 1:3:6 | Mass concrete | 4.44 | 0.462 | 0.924 |
In Indian practice these volume ratios are commonly used as nominal mixes for roughly M20, M15 and M10 concrete. IS 456:2000, the Indian code for plain and reinforced concrete, allows nominal mixes only for grades M20 and below, specifies them by mass rather than volume (Table 9), and states that design mix concrete is preferred. Anything structural above M20 needs a design mix.
How to use the calculator
- Measure the length, width and depth of the pour and enter them, choosing a unit for each.
- Leave the mix ratio on "Volume only" if you're ordering ready-mix, since the supplier batches the materials.
- Choose a mix ratio if you're mixing on site, and set wastage to suit your conditions.
- Read off the volume and, if selected, the cement bags, sand and aggregate.
For an L-shaped or irregular area, split it into rectangles, calculate each one, and add the results.
Related calculators
- RCC slab calculator: the same estimate set up for slab length, width and thickness in millimetres.
- Floor concrete calculator: concrete for a ground-floor bed.
- Column calculator: volume for rectangular, square and circular columns.
- Volume converter: convert cubic metres to cubic yards, litres or gallons.
These figures are estimates for ordering and budgeting. The concrete grade, thickness and reinforcement of any structural element should be specified by a qualified structural engineer under your local building code.
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