Concrete is sold by the cubic yard, but you measure in feet. Compute volume in cubic feet (length × width × thickness), divide by 27, and round up to order the right amount.
The example
20 × 10 ft slab, 4 in thick.
| A | B | |
|---|---|---|
| 1 | Item | Value |
| 2 | Area (ft²) | 200 |
| 3 | 4 in → yd³ | → 2.47 |
The formula
The formula:
How it works
How it works:
- Convert thickness to feet: inches ÷ 12 (a 4-inch slab is 0.333 ft).
- Multiply length × width × thickness for cubic feet.
- Divide by 27 — there are 27 cubic feet in a cubic yard.
- Round up and add a small waste allowance (5–10%) for spillage and uneven subgrade.
Add a safety margin. Running short mid-pour means a cold joint or an emergency second truck. Most estimators order =ROUNDUP(yards * 1.10, 2) — a 10% cushion — or round up to the nearest quarter-yard the supplier delivers. Over-ordering a little is far cheaper than coming up short.
Try it: interactive demo
Length, width (ft) and thickness (in).
Variations
With 10% waste
Safety margin:
Bags for small jobs
From cu ft:
Cost of pour
Yards × price:
Pitfalls & errors
Convert thickness. Inches must become feet (÷12) before multiplying.
27, not 9. A cubic yard is 27 cubic feet (3³), not 9.
Order a cushion. Round up and add waste — running short mid-pour is costly.
Practice workbook
Frequently asked questions
How do I calculate cubic yards of concrete in Excel?
How many cubic feet are in a cubic yard?
Should I add waste to a concrete order?
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