This concrete calculator tells you how much concrete a project needs before you order. Choose a rectangular slab, footing or wall, or a round column. Then enter the size in feet and inches, and the calculator shows the volume in cubic feet and cubic yards.
If you are not sure about the ground underneath, add an extra percentage for spills and uneven ground. The result updates as you type, so you can try different sizes quickly.
How to use the concrete calculator
- Choose the shape: slab, footing or wall (rectangle), or round column.
- Enter the length and width in feet for a rectangle, or the diameter in inches for a round column.
- Enter the thickness or depth in inches for a rectangle, and the height or depth in feet for a column.
- If you are pouring more than one of the same piece, enter how many in the count box.
- Optionally, enter an extra percentage for spills and uneven ground.
- Read the volume in cubic yards for ordering and cubic feet for checking your figures.
The formula
- Cubic feet = length × width × thickness × how many, with lengths in feet (inches ÷ 12)
- Cubic yards = cubic feet ÷ 27 (a cubic yard is 3 ft × 3 ft × 3 ft)
- Round: volume = 3.14159 × (diameter ÷ 2)² × height × how many
- With the extra: multiply by (1 + extra % ÷ 100)
Worked example
The figures below are made up to show the maths. They are not current prices, rates or product figures.
| Shape | Slab, footing or wall (rectangle) |
|---|---|
| Length | 20 ft |
| Width | 10 ft |
| Thickness or depth | 4 in |
| How many of them | 1 |
| Extra for spills and uneven ground | 5% |
- Volume 2.59 cubic yards
- Volume 70.00 cubic feet
Tips for an accurate answer
- Measure the thickness in inches, not feet. The calculator converts it for you, but entering feet by mistake will give a very wrong answer.
- Measure the diameter of a round column across the widest point, then enter that full width. The calculator halves it to find the radius.
- Add a little extra for spills and uneven ground, especially on soil that is not level.
- Check the dimensions against your plan before you order, and round up rather than down when a measurement falls between two sizes.
- If your project has several different pieces, run each one separately and add the results together.
Questions people ask
What units does the calculator use?
Length and width are entered in feet, thickness or depth in inches, column diameter in inches, and column height in feet. The results are shown in cubic feet and cubic yards. A cubic yard is 3 feet by 3 feet by 3 feet.
Why does the calculator show both cubic feet and cubic yards?
Cubic feet is useful for checking your own working, while cubic yards is the unit most concrete suppliers use for ordering. Both figures describe the same volume.
What should I enter for the extra percentage?
The extra percentage covers spills, waste and uneven ground. Enter it as a whole number, such as 5 for five percent. Leave it blank if you do not want any allowance added.
Can I calculate several pieces at once?
Yes, use the how many box to multiply one shape by a count. For example, a worked example with 1 slab and 5% extra gives 2.59 cubic yards, or 70.00 cubic feet. If your project has different shapes, calculate each one and add the totals.
Does this calculator tell me the cost of the concrete?
No. It works out the volume only. Ask your supplier for prices, as they depend on your location, the mix and delivery arrangements, and this page does not show any prices.
Sources
- 1 foot = 0.3048 metre exactly, so 1 inch (a twelfth of a foot) = 2.54 cm. Source: NIST, Revised unit conversion factors (the international foot).
- 1 yard = 0.9144 metre (3 feet). Source: NIST, NIST Guide to the SI, Appendix B.8: Factors for units listed alphabetically.
An estimate from the numbers you enter, worked out with the formula shown. Check quantities with your supplier before you order. Formulas and examples reviewed 24 Oct 2026. Read the disclaimer