What This Calculator Does
Square feet measure a flat area, while cubic feet measure a three-dimensional volume. To turn a square-foot measurement into cubic feet you simply need one more dimension: the depth, height, or thickness of the material. This calculator multiplies your area by that depth to give you the total volume in cubic feet (and conveniently in cubic yards as well).
How to Use It
Enter the floor area in square feet — for example the surface of a patio, garden bed, or room. Then enter the depth or height in feet. If your depth is in inches, divide by 12 first (a 3-inch layer is 0.25 ft). Click calculate and you get the volume in cubic feet, plus cubic yards for ordering bulk materials like concrete, soil, gravel, or mulch.
The Formula Explained
The relationship is direct:
$$\text{Cubic Feet} = \text{Area (ft}^2\text{)} \times \text{Depth (ft)}$$Because area already accounts for length × width, multiplying by a single depth value completes the third dimension. To convert to cubic yards, divide cubic feet by 27, since a cubic yard is \(3\,\text{ft} \times 3\,\text{ft} \times 3\,\text{ft} = 27\,\text{ft}^3\).
Worked Example
Suppose you have a 120 ft² patio and want a 4-inch concrete slab. Four inches is \(4 \div 12 = 0.333\,\text{ft}\). Volume:
$$120 \times 0.333 = 40\,\text{ft}^3$$Dividing by 27 gives about 1.48 cubic yards of concrete to order.
FAQ
Can I convert square feet to cubic feet without depth? No. Square feet is area only; you must supply a depth, height, or thickness to obtain a volume.
What if my depth is in inches? Divide inches by 12 to convert to feet before entering it.
How do I get cubic yards? Divide the cubic-feet result by 27 — this calculator does it for you automatically.
