Litre Volume of a Cylinder

The maths in one line

The volume of a cylinder is:

A worked example

Worked example. Take a cylinder with a diameter of 15 cm (so a radius of 7.5 cm) and a height of 30 cm. The base area is π × 7.5² = 176.71 cm², and multiplying by the height gives a volume of about 5.30 litres (5,301 cm³ · 1.40 US gallons).

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

How the calculation works

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:

What if my measurements are in millimetres?

Pick mm on each field. The tool converts to metres internally, so you can measure a small part in millimetres and still read a clean litre result without converting by hand.

What is that in US or Imperial gallons?

The litre result sits beside its gallon equivalents in the breakdown, so you can convert on the spot: 1000 litres is about 264 US gallons or 220 Imperial gallons.

How many millilitres or cubic centimetres is it?

One litre is exactly 1000 millilitres and 1000 cubic centimetres, so the mL and cm3 figures are just the litre value in disguise, and all three appear together in the result.

How do I size an aquarium properly?

Measure the inside dimensions and the water height, not the glass. The litre figure guides dosing and heater sizing, but leave a few centimetres of freeboard at the top so nothing overflows.

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 tank capacity volume formula. These related calculators pick up where this one leaves off:

When this comes in handy

People reach for this in a range of situations:

• Filling an aquarium to the right level
• Batch-sizing in a home brewery or kitchen
• Sizing a rainwater butt in litres
• Dosing chemicals for a metric tank

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.

Good to know