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Cubic feet calculator
Work out the cubic feet inside any cylinder from feet or inches, with the conversion to gallons and litres alongside.
Cubic feet is the unit of choice for larger cylinders — storage tanks, silos, concrete forms — and this cubic feet calculator gives it to you directly. Measure in feet (or inches, and let the tool convert), and read the ft³ result with gallons alongside.
Using the calculator
- Measure across the circular end — the diameter or radius.
- If you measured the diameter, halve it to get the radius r.
- Square the radius and multiply by π to get the base area.
- Multiply the base area by the height h: V = π r² h.
- Convert the result into your preferred unit above.
Worked example. Take a cylinder with a diameter of 1.5 ft (so a radius of 0.75 ft) and a height of 5 ft. The base area is π × 0.75² = 1.77 ft², and multiplying by the height gives a volume of about 8.84 cubic feet (66.1 US gallons · 250 litres).
| From | To | Multiply by |
|---|---|---|
| cm³ | litres | 0.001 |
| litres | m³ | 0.001 |
| in³ | US gallons | ÷ 231 |
| ft³ | US gallons | 7.4805 |
| ft³ | litres | 28.3168 |
For anything that holds liquid, measure the inside of the cylinder — the wall takes up space that the contents cannot.
Every cubic feet page
Each page below targets a specific question and opens with the calculator ready to go:
Questions people ask
What is the formula for the volume of a cylinder?
V = π r² h — the area of the circular base (π r²) multiplied by the height (h). If you have the diameter instead of the radius, halve it first: r = d ÷ 2.