Contractor & construction
Concrete Calculator
Works concrete volume, where the conversion to cubic yards and the waste both matter.
Result
Ready-mix is sold in whole or half yards and most suppliers charge a short-load fee under about 3 yards. Always order slightly over. A pour that runs short mid-way is far more expensive than surplus concrete.
Get a Free Business AuditHow the calculation works
Length times width times thickness gives volume, converted to cubic yards by dividing by twenty-seven when the dimensions are in feet. A ten by ten foot area at four inches is 33.33 cubic feet, which is 1.24 cubic yards, and a waste allowance is added on top before ordering.
What moves the number
- Thickness, which is frequently stated in inches against dimensions in feet.
- Waste allowance for spillage and uneven subgrade.
- Subgrade variation, which increases actual volume.
- Supplier minimum load and short-load charges.
Where this one goes wrong
An uneven or soft subgrade consumes more concrete than the calculation suggests, sometimes considerably, because the pour fills the low spots and the thickness is a minimum rather than an average. Allow for it and compact the base properly. Ready-mix suppliers also have minimum loads and charge for short loads, which means ordering slightly over is usually cheaper than a second delivery for a shortfall.
Before you quote
- Convert inches of thickness to feet before multiplying.
- Allow extra for subgrade variation, not just spillage.
- Check the supplier's minimum load and short-load charge.
Questions
About this calculator
How do I convert to cubic yards?
Divide cubic feet by twenty-seven. With dimensions in feet and thickness in inches, convert the thickness first: four inches is one third of a foot, so a ten by ten area at four inches is 33.33 cubic feet or about 1.24 cubic yards.
Why does a pour use more than calculated?
An uneven or soft subgrade fills the low spots, so the stated thickness is a minimum rather than an average. Compacting the base properly reduces it, and allowing for it in the order avoids running short mid-pour.
Is it better to over-order or under-order?
Over-order modestly, because a second delivery for a shortfall costs a short-load charge and a delay while the first pour starts setting. Suppliers have minimum loads, which makes the marginal cost of a little extra small.
The formula
cubic yards = length × width × (depth ÷ 12) ÷ 27
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How to use this calculator
- Length (ft) (ft). Enter your own figure; the page starts at 30 ft.
- Width (ft) (ft). Enter your own figure; the page starts at 20 ft.
- Thickness (inches) (in). Enter your own figure; the page starts at 4 in.
- Waste / compaction allowance (%). Enter your own figure; the page starts at 10%.
- Cost per cubic yard delivered ($). Enter your own figure; the page starts at $165.
The result updates as you type, so you can try a figure, see what it does to cubic yards needed, and change it back. Nothing you enter is sent anywhere or saved.
A worked example
These are the figures the calculator opens with. Every number in the results column below is produced by the same calculation the page runs, so you can follow it through before putting your own figures in.
What goes in
| Input | Value |
|---|---|
| Length (ft) | 30 ft |
| Width (ft) | 20 ft |
| Thickness (inches) | 4 in |
| Waste / compaction allowance | 10% |
| Cost per cubic yard delivered | $165 |
What comes out
| Result | Value |
|---|---|
| Cubic yards needed main result | 8.1 |
| Cubic feet | 220.0 |
| Approximate tons | 16.5 |
| Estimated cost | $1,344 |
| 80 lb bags (small pours) | 367 |
This pour needs 8.1 cubic yards, about $1,344 delivered, or 367 80 lb bags if you are mixing on site.
How sensitive the answer is
Holding everything else steady and changing only cost per cubic yard delivered, this is what happens to cubic yards needed. It is worth knowing which of your inputs the answer actually hinges on, and which barely move it.
| Cost per cubic yard delivered ($) | Cubic yards needed |
|---|---|
| $83 | 8.1 |
| $124 | 8.1 |
| $165 example above | 8.1 |
| $248 | 8.1 |
| $330 | 8.1 |
Every other input is held at the example value while this one changes, which is not how a real job behaves. Treat it as a guide to which number matters most, not as five separate quotes.
What each figure means
- Length (ft) (ft)
- Measured in ft, starting at 30 ft.
- Width (ft) (ft)
- Measured in ft, starting at 20 ft.
- Thickness (inches) (in)
- Measured in in, starting at 4 in.
- Waste / compaction allowance (%)
- A percentage, between 0 and 60, starting at 10%.
- Cost per cubic yard delivered ($)
- A money amount, starting at $165.
What the results tell you
| Result | What it is |
|---|---|
| Cubic yards needed | The headline result. A decimal figure. |
| Cubic feet | A decimal figure. |
| Approximate tons | A decimal figure. |
| Estimated cost | A money figure. |
| 80 lb bags (small pours) | A number. |
Overhead is where these go wrong
Pricing and margin figures are only as good as the cost you put in. If your cost covers parts and wages but not the van, the insurance, the phone and the unbilled hours, the markup is paying for those before it becomes profit, and the margin you think you are making is not the one you are making.
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