Cubic feet
How to Calculate 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.
Cubic feet is the unit of choice for larger cylinders — storage tanks, silos, concrete forms — and this how to calculate cubic feet of a cylinder gives it to you directly. Measure in feet (or inches, and let the tool convert), and read the ft³ result with gallons alongside.
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 maths in one line
The volume of a cylinder is:
V = π r² hA worked example
Worked example. Take a cylinder with a diameter of 2 ft (so a radius of 1 ft) and a height of 4 ft. The base area is π × 1² = 3.14 ft², and multiplying by the height gives a volume of about 12.57 cubic feet (94.0 US gallons · 356 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.
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.
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.
Follow-on questions, answered
Most jobs need one or two more things once the volume lands. The common follow-ups, with the numbers you need, are below:
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.
Where people go wrong
The commonest slip is using the diameter where the formula wants the radius, which on its own quadruples the base area. Close behind is mixing units, such as a radius in centimetres with a height in metres. Keep every length in the same unit, or let the tool convert, and double-check whether you measured to the centre or across the whole width. When a figure looks surprising, that width measurement is almost always where the problem is hiding, so re-read it first.
Reading and converting your result
One number, many units. Whatever you enter, the result lists the same volume as litres, US gallons, Imperial gallons, millilitres, cubic centimetres, cubic inches, cubic feet, cubic yards and cubic metres at the same time. You almost never have to convert by hand: read the figure in the unit your job uses and copy any of the others straight from the breakdown. If you need a shareable version, the copy-link button preserves your exact inputs so a colleague opens the page with the same calculation already filled in.
Keep going
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:
When this comes in handy
People reach for this in a range of situations:
- Ordering concrete for a round column or footing
- Sizing a silo or bulk storage cylinder
- Estimating air volume in a round duct
In short: measure the width and the height, keep them in the same unit, and the tool turns them into a volume you can read in litres, gallons, cubic feet or anything else, with the working shown so you can trust it. If a result ever looks off, re-enter the measurement you are least sure of, or switch to the diameter input and let the tool halve it for you, which catches the most common error before it matters.
Frequently asked questions
Do I use radius or diameter?
What units can I use?
Is the volume of a cylinder squared or cubed?
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.