Add the lengths of all strip footings, ground beams or beam sections with the same cross-section.
The calculator uses a true cylinder. Enlarged pile bases, irregular bores and collapsed ground are not included.
The result includes the sloping in-situ stair waist, the concrete forming the steps above it and any selected landings.
Additional settingsStrength class, density and bag yield
C20/25 is a commonly encountered strength class, but suitability depends on the specification, loads and exposure. This selector does not design the concrete.
Important: strength class and bag yield are separate product data. Enter the finished yield and water amount shown on the actual bag or technical data sheet. The declared mixed yield already includes the added water, so do not add that water volume again.
One or more values are invalid.
Which concrete calculator should I use?
Use this page when you know the dimensions and need the concrete volume. If the volume is already known, use the mix ratio calculator instead.
Concrete Calculator
Choose this calculator when the slab, footing, column, pile or stair dimensions are known but the volume in m³ is not.
Concrete Mix Ratio Calculator
Choose this when you already know the required m³ and plan to mix a small quantity on site. It estimates cement, sharp sand, coarse aggregate and water.
How do you calculate concrete in cubic metres?
Convert all dimensions to metres, calculate the geometric volume and only then add any chosen waste allowance.
Measure the construction
Enter length and width in metres and slab thickness or column and pile diameters in centimetres. The calculator converts the units automatically.
Choose the correct shape
Rectangular elements use length × width × depth. Circular elements use the cylinder formula based on radius.
Allow for site conditions
Theoretical volume does not include uneven formation, irregular bores, pump residue, spillage or formwork tolerances.
Check before ordering
Confirm the ready-mixed concrete quantity and delivery conditions with the supplier. For bagged concrete, always use the yield printed on the chosen product.
How much concrete is needed for a 100 m² slab?
The table shows geometric volume without a waste allowance. Slab thickness must be specified for the project, not selected from this table.
| Slab area | Thickness | Concrete volume | Estimated weight at 2,400 kg/m³ |
|---|---|---|---|
| 100 m² | 8 cm | 8 m³ | 19.2 t |
| 100 m² | 10 cm | 10 m³ | 24.0 t |
| 100 m² | 12 cm | 12 m³ | 28.8 t |
| 100 m² | 15 cm | 15 m³ | 36.0 t |
| 100 m² | 20 cm | 20 m³ | 48.0 t |
Concrete strength classes under BS EN 206-1
The uses below are broad context only. BS EN 206-1:2026 is the new European edition. The current BS 8500:2023 series was prepared alongside the preceding BS EN 206:2013+A2:2021, so the project specification should identify the applicable editions during the transition.
| Class | Cylinder strength | Cube strength | Broad context only |
|---|---|---|---|
| C8/10 | 8 MPa | 10 MPa | Blinding and non-loadbearing fill where specified |
| C12/15 | 12 MPa | 15 MPa | Blinding, bases and lightly loaded non-structural work where specified |
| C16/20 | 16 MPa | 20 MPa | Lightly loaded work and bases subject to the specification |
| C20/25 | 20 MPa | 25 MPa | A commonly encountered structural class; suitability still depends on exposure and design |
| C25/30 | 25 MPa | 30 MPa | Often specified for structural work; not an automatic choice for footings or stairs |
| C30/37 | 30 MPa | 37 MPa | Higher design strength where required by the specification |
What does C25/30 mean?
The letter C denotes a compressive strength class for normal-weight or heavyweight concrete. The first number is the characteristic strength of a 150 × 300 mm cylinder and the second of a 150 mm cube, in MPa, normally at 28 days.
C25/30 is therefore one class, not a choice between 25 and 30: it denotes 25 MPa cylinder strength and 30 MPa cube strength.
What is bagged premixed concrete?
Here, bagged premixed concrete means a factory-blended dry product containing cement, aggregates and possible additions. On site, add only the amount of water stated on the bag or technical data sheet.
It is not a bag of cement. Cement bought on its own still needs suitable sharp sand, coarse aggregate, water and a verified mix design.
Is the construction type enough to select a class?
No. Selection also depends on loads, exposure, moisture, carbonation, chlorides, freeze–thaw action, chemical attack, reinforcement cover and design working life.
Exposure designations such as XC, XD, XS, XF and XA describe different environments. Two visually similar elements can therefore require different concrete.
Does a higher class always need more bags?
No. Bag quantity is determined by the product's finished yield in litres, not by the C class alone. Products of equal bag weight can have different yields.
Do not confuse concrete classes such as C20/25 or C25/30 with screed designations such as CT-C25-F4 under BS EN 13813. They are different classification systems.
Concrete volume for slabs and strip footings
For a rectangular slab, multiply length, width and thickness. The same geometry works for floors, shed bases, paths, pads and rectangular foundation slabs. For a circular slab, calculate the circle area and multiply by thickness.
For strip footings or ground beams, enter the total length of sections that share one width and depth. Where the cross-section changes, calculate each part separately and add the volumes.
Concrete for columns, piles and post holes
Rectangular columns use section area × height × quantity. Circular columns and cylindrical piles use π × r² × h, with diameter divided by two to obtain the radius.
Pile volume is theoretical: actual bore diameter and depth can vary and loose ground may collapse. Pile dimensions, reinforcement and concrete specification must come from the design.
How much concrete is needed for in-situ stairs?
The stair calculation adds the sloping waist slab, the triangular wedges forming the steps and any rectangular landings. The result breakdown shows the combined volume.
This is a material quantity tool, not a stair design tool. Geometry, span, support, reinforcement and load capacity require competent design.
Concrete weight and bagged mix quantity
Estimated weight is volume multiplied by the selected density. The default 2,400 kg/m³ is only a working estimate for normal-weight concrete; lightweight and heavyweight concrete differ substantially.
Bagged premixed concrete is calculated from the finished mixed yield, not by adding dry product volume to water volume. The default 25 kg bag, 12.5 L yield and 3 L water are editable demonstration values only.
Strength class does not determine a particular bag's yield. Before purchase, enter the yield and mixing water from the selected bag or technical data sheet.
Strength-class notation is explained using BS EN 206-1:2026. BS 8500:2023 remains the current complementary UK series but was prepared with the preceding BS EN 206 edition, so the project or contract must identify the applicable documents. Density and bag-yield values are estimates and must be checked against the supplier’s data. This calculator does not produce a structural design or demonstrate standards compliance.
Frequently asked questions about concrete quantities
Answers about cubic metres, weight, waste allowance, footings, piles and bagged concrete.