What This Calculator Does
This calculator finds the volume of a cylinder expressed in cubic feet (ft³). You provide the cylinder's diameter and height in feet, and it returns the total internal volume — handy for sizing tanks, pipes, silos, columns, water heaters, and concrete pours. It works for any units of measurement as long as they are in feet; if your dimensions are in inches, divide by 12 first.
How to Use It
Enter the diameter across the circular face of the cylinder and the height (or length) of the cylinder, both in feet. Click calculate to see the volume in cubic feet along with the computed radius. For a tank measured in inches, convert each measurement to feet first (inches ÷ 12).
The Formula Explained
A cylinder's volume equals the area of its circular base multiplied by its height. The base area of a circle is \(\pi r^2\), where \(r\) is the radius. So the full formula is $$V = \pi \times r^2 \times h$$ Because diameter is easier to measure than radius, this tool takes the diameter and halves it: \(r = d \div 2\).
Worked Example
Suppose a cylindrical tank has a diameter of 2 ft and a height of 5 ft. The radius is \(2 \div 2 = 1\) ft. The volume is $$V = \pi \times 1^2 \times 5 = \pi \times 5 \approx 15.708 \text{ cubic feet}.$$ That means the tank holds about 15.71 ft³.
FAQ
How do I convert cubic feet to gallons? Multiply cubic feet by 7.48 to get US gallons. The example above (15.708 ft³) is about 117.5 gallons.
My measurements are in inches — what do I do? Divide each measurement by 12 to convert to feet before entering them, since this calculator expects feet.
Does it matter whether I call it height or length? No. For a horizontal cylinder, the "height" field is simply the length along the axis; the formula is the same.
