Cubic feet
Cubic Foot of a Cylinder
Work out the cubic feet inside any cylinder from feet or inches, with the conversion to gallons and litres alongside.
This cubic foot 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.
For bigger cylinders the numbers get unwieldy in small units, which is exactly why cubic feet exists. A round column that would be tens of thousands of cubic inches becomes a handful of cubic feet — easier to picture, and easier to price.
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 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.
Conversions use standard factors: 1 US gallon = 231 in³, 1 Imperial gallon = 4.54609 L, 1 litre = 1000 cm³.
How the calculation works
- 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.
Once the result is in
The figure above is usually the start, not the finish. These are the questions that tend to come next, answered here so you do not have to run another search:
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.
Getting it right
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.
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:
When this comes in handy
A few of the jobs it gets used for:
- Ordering concrete for a round column or footing
- Sizing a silo or bulk storage cylinder
- Estimating air volume in a round duct
To sum up, the whole job is two measurements and one formula. Enter them above, pick your unit, and you have an accurate figure plus every equivalent unit beside it. Keep a copy with the copy-result button, save the shareable link if someone else needs the same numbers, and use the history panel to compare a few options without starting from scratch.
Questions people ask
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.