How to Calculate Concrete
Concrete volume is calculated by multiplying the length, width, and depth of the area being poured. Because concrete is commonly ordered by the cubic yard, the final cubic-foot volume is divided by 27.
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Concrete Calculator
Calculate how much concrete you need for slabs, footings, walls, and other common concrete projects.
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Concrete calculator
Driveways, patios, floors and pads
Enter valid dimensions to see your result.
Concrete Calculator Formula
Length × Width × Depth = Cubic Feet
Cubic Feet ÷ 27 = Cubic Yards
Convert depth to feet when it is measured in inches: 4 in ÷ 12 = 0.333 ft.
Concrete Calculation Example
A slab that is 20 ft long, 30 ft wide, and 4 in thick:
20 × 30 × (4 ÷ 12) = 200 cubic feet
200 ÷ 27 = 7.41 cubic yards
Concrete needed: 7.41 yd³7.41 × 1.10 = 8.15 yd³
With 10% extra: approximately 8.15 yd³Common Concrete Calculations
Concrete Slabs
Driveways, patios, floors, pads, and walkways.
Concrete Footings
Continuous and isolated foundation footings.
Concrete Walls
Foundation and retaining walls.
Concrete Columns
Posts, piers, and round columns.
How Much Extra Concrete Should I Order?
Many concrete orders include a small additional amount to account for uneven excavation, spillage, form variation, and other jobsite conditions. A common planning allowance is around 5%–10%, depending on the project.
For large or critical pours, confirm quantities with the concrete supplier or project professional before ordering.
Concrete Quick Reference
| Measurement | Equivalent |
|---|---|
| 1 cubic yard | 27 cubic feet |
| 1 cubic foot | 1,728 cubic inches |
| 4 in | 0.333 ft |
| 6 in | 0.5 ft |
| 8 in | 0.667 ft |
| 12 in | 1 ft |
Concrete Calculator FAQ
How many cubic feet are in a cubic yard of concrete?
One cubic yard contains 27 cubic feet.
How do I calculate concrete for a slab?
Multiply the slab's length by width by thickness to get its volume. Convert the thickness to feet, then divide the cubic-foot volume by 27 to get cubic yards.
How do I convert concrete thickness from inches to feet?
Divide the number of inches by 12. For example, 4 inches is approximately 0.333 feet and 6 inches is 0.5 feet.
Should I order extra concrete?
A small allowance is commonly added for jobsite variation and waste. Many estimates use roughly 5%–10%, but the appropriate amount depends on the project.
How much does one cubic yard of concrete cover?
Coverage depends on thickness. One cubic yard covers about 81 square feet at 4 inches thick, about 54 square feet at 6 inches thick, and about 40.5 square feet at 8 inches thick.
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