How to calculate yards of concrete
Begin with the square footage, then multiply it by the depth in inches. Divide that total first by 12 and then by 27. Input the area and thickness to get your total.
What area can one yard of concrete cover?
| Thickness | Square feet per yard | With 10% extra | Square meters per yard |
|---|---|---|---|
| 3 in | 108 | 98 | 10.0 |
| 4 in | 81 | 74 | 7.5 |
| 5 in | 64.8 | 59 | 6.0 |
| 6 in | 54 | 49 | 5.0 |
| 8 in | 40.5 | 37 | 3.8 |
One cubic yard holds 27 cubic feet, and at a depth of 1 inch it covers 324 square feet. Take 324 and divide it by the thickness in inches.
Concrete yardage calculator formula in three steps
- Find the square footage by multiplying the length and width, with both measurements in feet. A slab measuring 12 by 16 ft has an area of 192 square feet.
- Multiply the area by the thickness in inches, then divide by 12 to find cubic feet. An area of 192 square feet at a thickness of 4 inches equals 64 cubic feet.
- Divide by 27 to get cubic yards, then include 5 to 10% extra for spills and uneven ground. The volume of 64 cubic feet equals 2.37 cubic yards. Including 10% extra brings the amount to 2.61.
Examples of calculations
- A footing measuring 40 ft long, 16 in wide and 8 in deep needs 35.56 cubic feet. Use 40 × 16 ÷ 12, then multiply by 8 ÷ 12. Before adding extra, this volume comes to 1.32 cubic yards.
- A round pier that's 12 in wide and 48 in deep holds 0.12 cubic yards. Multiply 3.1416 by 0.5, then by 0.5, then by 4 for 3.14 cubic feet. The radius in feet is 0.5.
- A slab that measures 100 square feet and is 4 in thick has a volume of 100 × 4 ÷ 12 = 33.3 cubic feet, which gives 1.23 cubic yards. Adding 10% extra changes the amount to 1.36.
Where the calculation breaks down
The measurement people get wrong is the thickness. At a depth of 4 inches, adding another quarter inch requires 6.25% more concrete, which is more than half of the usual 10% allowance. Measure the depth of your forms in several places, then use the deepest number you find.