How to Calculate Cubic Feet of Cylinder

How the volume is worked out

The volume of a cylinder is:

A 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).

Conversions use standard factors: 1 US gallon = 231 in³, 1 Imperial gallon = 4.54609 L, 1 litre = 1000 cm³.

How to work it out

1. Measure across the circular end — the diameter or radius.
2. If you measured the diameter, halve it to get the radius r.
3. Square the radius and multiply by π to get the base area.
4. Multiply the base area by the height h: V = π r² h.
5. 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

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.

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.

Getting the number in the unit you need

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.

What to work out next

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

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

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.

Good to know