Cubic feet
Calculate the Cubic Feet of a Cylinder
Work out the cubic feet inside any cylinder from feet or inches, with the conversion to gallons and litres alongside.
This calculate the cubic feet of a cylinder answers a practical question: how many cubic feet does this cylinder contain? Enter the diameter and height, and the tool returns ft³, plus the gallon and litre equivalents for good measure.
Cubic feet is the working unit for anything large and dry — silo capacity, duct sizing, the concrete in a round pier. It sits neatly between inches and yards, so most builders measure in feet, calculate in cubic feet, and only convert to yards or gallons at the very end.
The formula behind it
The volume of a cylinder is:
V = π r² hA worked example
Worked example. Take a cylinder with a diameter of 3 ft (so a radius of 1.5 ft) and a height of 6 ft. The base area is π × 1.5² = 7.07 ft², and multiplying by the height gives a volume of about 42.41 cubic feet (317.3 US gallons · 1,201 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.
Conversions use standard factors: 1 US gallon = 231 in³, 1 Imperial gallon = 4.54609 L, 1 litre = 1000 cm³.
How to work it out
- 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.
Getting an accurate measurement
If you can only reach the top, measure the diameter across the opening and halve it. Keep every measurement in the same system, and let the tool convert between units for you.
What people work out next
To save you a second search, here are the related answers people most often want straight after this calculation:
How much concrete should I order?
Suppliers sell by the cubic yard, and 27 cubic feet make one cubic yard. Work in cubic feet here, then divide by 27, or use the cubic-yards mode directly for the order.
What is it in litres or cubic metres?
One cubic foot is about 28.32 litres, or 0.0283 cubic metres, and both appear alongside the cubic-foot result for metric jobs.
Do I measure in feet or inches?
Either. Enter inches on each field if that is how you measured, and the tool converts to feet before giving you the cubic-foot answer.
How many gallons is that?
One cubic foot holds about 7.48 US gallons, and the gallon value is shown in the breakdown, so a cubic-foot figure converts into a fill quantity instantly.
Common mistakes to avoid
Two things trip people up: squaring the wrong number, and forgetting that the answer is cubic. If a result looks four times too big or too small, you have probably swapped radius and diameter somewhere, so it is always worth re-reading the measurement you are least sure of. It also helps to glance at the equivalent units; if the litre and gallon figures are both off by the same factor, the input is the culprit, not the maths.
Getting the number in the unit you need
Showing every unit at once is about speed and safety: you see the answer in litres, gallons and cubic feet side by side, so there is no chance of applying the wrong conversion factor. Change the output unit at the top to make any of them the headline figure, switch the precision to exact if you want the value in terms of pi, and use copy-result to paste a tidy summary wherever you need it.
Related things you might need
Once you have your answer you may also want to work in gallons cubic yards tank capacity. These related calculators pick up where this one leaves off:
Common uses
It comes in handy across quite different tasks:
- Ordering concrete for a round column or footing
- Sizing a silo or bulk storage cylinder
- Estimating air volume in a round duct
The bottom line: with the radius or diameter and the height, the volume follows immediately, and the breakdown lets you hand the same number to anyone in the unit they prefer. Measure inside dimensions for anything that holds liquid, leave a little headspace at the top of a real container, and treat the geometric figure as a clean maximum rather than the final word on usable capacity.
Frequently asked questions
Does this work for a tank or a pipe?
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.