Concrete & construction
Concrete Yard Calculator
Converts dimensions to cubic yards, where the thickness unit is the usual error.
Result
Concrete is ordered by the cubic yard and delivered in fixed increments, so the figure you order is always rounded up. Most crews add 5% to 10% for spillage, uneven subgrade and over-excavation; running short mid-pour is far more expensive than a little waste.
Get a Free Business AuditHow the calculation works
Length times width times thickness gives cubic feet, divided by twenty-seven for cubic yards. With dimensions in feet and thickness in inches, the thickness converts 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.
What moves the number
- Thickness, converted from inches to feet.
- Area dimensions.
- Waste allowance on top of the calculated volume.
- Subgrade variation, which increases actual volume.
Where this one goes wrong
Multiplying feet by inches without converting produces a figure twelve times too large, which is obvious at a glance on a small pour and less so on a large one where nobody checks. Convert first. The calculated volume is also a minimum rather than an order quantity, since an uneven subgrade fills low spots and the stated thickness becomes an average rather than a floor.
Before you quote
- Convert thickness from inches to feet before multiplying.
- Divide cubic feet by twenty-seven for cubic yards.
- Add a waste allowance before ordering.
Questions
About this calculator
How many cubic feet in a cubic yard?
Twenty-seven, since a yard is three feet and the conversion is cubed. That is the division that turns a volume in cubic feet into the unit ready-mix is ordered in, and forgetting it produces a figure twenty-seven times too large.
How do I handle thickness in inches?
Convert it to feet first by dividing by twelve. 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. Multiplying feet by inches gives a figure twelve times too large.
Should I order exactly the calculated amount?
No, add a waste allowance, because the calculated volume is a minimum and an uneven subgrade consumes more. Running short mid-pour costs a short-load charge and leaves a joint where you did not want one.
The formula
cubic yards = length x width x (thickness / 12) / 27
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How to use this calculator
- Length (ft) (ft). Enter your own figure; the page starts at 20 ft.
- Width (ft) (ft). Enter your own figure; the page starts at 12 ft.
- Thickness (in) (in). Enter your own figure; the page starts at 4 in.
- Waste allowance (%). Enter your own figure; the page starts at 8%.
- Price per cubic yard ($). 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 to order, 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) | 20 ft |
| Width (ft) | 12 ft |
| Thickness (in) | 4 in |
| Waste allowance | 8% |
| Price per cubic yard | $165 |
What comes out
| Result | Value |
|---|---|
| Cubic yards to order main result | 3.3 |
| Net volume | 3.0 |
| Volume | 80.0 |
| Estimated concrete cost | $536.25 |
| Slab area | 240.0 |
That slab is 3.0 cubic yards net. Order 3.3 yards with 8% waste, about $536.25 of concrete.
How sensitive the answer is
Holding everything else steady and changing only price per cubic yard, this is what happens to cubic yards to order. It is worth knowing which of your inputs the answer actually hinges on, and which barely move it.
| Price per cubic yard ($) | Cubic yards to order |
|---|---|
| $83 | 3.3 |
| $124 | 3.3 |
| $165 example above | 3.3 |
| $248 | 3.3 |
| $330 | 3.3 |
Every other input is held at the example value while this one changes, which is not how a real job behaves. Treat it as a guide to which number matters most, not as five separate quotes.
What each figure means
- Length (ft) (ft)
- Measured in ft, starting at 20 ft.
- Width (ft) (ft)
- Measured in ft, starting at 12 ft.
- Thickness (in) (in)
- Measured in in, between 0 and 60, starting at 4 in.
- Waste allowance (%)
- A percentage, between 0 and 40, starting at 8%.
- Price per cubic yard ($)
- A money amount, starting at $165.
What the results tell you
| Result | What it is |
|---|---|
| Cubic yards to order | The headline result. A decimal figure. |
| Net volume | A decimal figure. |
| Volume | A decimal figure. |
| Estimated concrete cost | A money figure. |
| Slab area | A decimal figure. |
Order slightly more than this
Volume calculations assume a level, properly prepared base and exact dimensions. Sub-base variation, over-excavation and spillage all consume concrete, which is why most contractors add a margin. Running short mid-pour is far more expensive than a small overage.
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