Concrete volume
—
m³
Free tool
Concrete Calculator with a live 3D foundation preview
Estimate the concrete volume, cement, sand, gravel and number of bags you need for a slab, strip, column, or pile-and-beam foundation — and see the foundation in 3D as you type. Switch between metric and imperial, add a waste margin, and get an order-ready material list in seconds.
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Cement
—
kg
Bags
—
bags
Sand
—
m³
Gravel
—
m³
Estimated cost
—
total
How to use the concrete calculator
- Step 1
Pick your foundation type
Choose slab, strip, column, or pile + beam — the 3D preview updates to match.
- Step 2
Enter the dimensions
Add length, width, and thickness or height, in metric or imperial units.
- Step 3
Choose the concrete mix ratio
Select the ratio for your grade, e.g. 1:2:4 for general foundations.
- Step 4
Read the results
Get concrete volume, cement (kg + bags), sand and gravel, with your waste margin applied.
How the calculation works
The calculator first computes the wet concrete volume from your foundation geometry. Because concrete loses volume as water evaporates and the mix compacts, dry ingredients are scaled up by a dry-mix multiplier of 1.54.
The chosen mix ratio then splits that dry volume into cement, sand, and gravel. Cement volume is converted to weight using a density of 1400 kg/m³, then to 25 kg or 50 kg bags. Add a waste margin (5–10% is typical) so you order enough for spillage and uneven subgrade.
1.54 — Dry-mix multiplier
Wet concrete needs ~54% more dry ingredients, because water evaporates and the mix compacts as it cures.
1400 kg/m³ — Cement density
Standard Portland cement density, used to convert cement volume into weight and bag count.
Concrete mix ratio table
| Mix ratio | Typical grade | Common use |
|---|---|---|
| 1 : 1.5 : 3 | ~M20 / C20 | Structural slabs, columns, beams |
| 1 : 2 : 4 | ~M15 / C15 | General foundations, footings |
| 1 : 3 : 6 | ~M10 / C10 | Mass concrete, blinding, fill |
| 1 : 4 : 8 | ~M7.5 | Non-structural fill, levelling |
Grades are indicative; always follow your structural engineer's specification.
Worked example: concrete for a 5 × 4 × 0.2 m slab
A monolithic slab 5 m × 4 m × 0.2 m = 4 m³ of concrete. At a 1:2:4 mix with the 1.54 dry multiplier, that's about 1,230 kg of cement (~50 bags of 25 kg) before waste, plus roughly 1.76 m³ of sand and 3.52 m³ of gravel. Add 5% waste and you'd order for about 4.2 m³ — around 52 bags of cement.
Foundation types explained
Slab (monolithic)
A single continuous concrete plate poured over the building footprint. Simple to estimate — volume is length × width × thickness — and common for garages, extensions, and lightweight structures on stable ground.
Strip
Continuous strips of concrete running under load-bearing walls. Volume follows the wall perimeter × strip width × height, so it uses far less concrete than a full slab for the same footprint.
Column (isolated/pad)
Individual pads under columns or posts. Volume is width × length × height per pad, multiplied by the number of columns. Used where loads are concentrated at points rather than spread out.
Pile + beam
Deep piles transfer load to firmer strata, tied together by a ground beam. Volume combines the perimeter beam with the cylindrical piles — useful on weak or expansive soils.
Frequently asked questions
How much concrete do I need for a slab?
Multiply length × width × thickness. For example, a 5 m × 4 m slab at 0.2 m thick needs 4 m³ of concrete. Add a 5–10% waste margin before ordering, so a 4 m³ slab is ordered as roughly 4.2–4.4 m³.
How many bags of cement are in one cubic metre?
It depends on the mix ratio. For a typical 1:2:4 mix, one cubic metre of finished concrete needs roughly 320 kg of cement — about 13 bags of 25 kg or 7 bags of 50 kg. Richer mixes (e.g. 1:1.5:3) need more cement per cubic metre.
What concrete mix ratio should I use for foundations?
1:2:4 (≈M15/C15) is a common general-purpose foundation and footing mix. For structural slabs, columns, and beams a richer 1:1.5:3 (≈M20/C20) is typical. Always follow your structural engineer's specification — the ratio drives strength.
How much extra concrete should I order for waste?
Most professionals add 5–10% on top of the calculated volume to cover spillage, uneven subgrade, and over-excavation. This calculator lets you set the waste margin and applies it to every output.
What's the difference between slab, strip, column, and pile foundations?
A slab is one continuous plate over the footprint. A strip runs concrete under load-bearing walls only. Columns (pads) sit under individual posts. Pile + beam drives deep piles to firmer ground and ties them with a beam — chosen on weaker soils.
Does this calculator work in imperial units?
Yes. Toggle between metric and imperial: enter dimensions in feet and get volume in cubic yards, cement weight in pounds, and bag counts for 40 lb bags. The formulas and the 1.54 dry-mix multiplier stay the same.
From the field → PinMy
Calculating the pour is step one. On site, the questions come later: was the rebar placed right, did the formwork hold, where was that cold joint? With PinMy you pin a photo, a voice note or a video on the exact spot of your plan, photo, or 3D model — so the record of the pour lives in one place, not in WhatsApp.
Related
This calculator gives estimates for planning and ordering. Always confirm quantities and mix design with your structural engineer and concrete supplier.