Cubic feet
Cubic Feet 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 cubic feet 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.
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.
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.
Once the result is in
To save you a second search, here are the related answers people most often want straight after this calculation:
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.
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.
When this comes in handy
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
Common mistakes to avoid
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
Because volume units are where most errors creep in, the tool does the converting for you. Enter your measurements once and every common unit appears together, from millilitres up to cubic metres and across to US and Imperial gallons. Pick whichever the task calls for and lift the rest from the list; nothing needs a second calculation. The result also updates live as you change a measurement, so you can compare two sizes quickly without starting over.
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:
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.
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.