Volume in Gallons of a Cylinder Calculator

The maths in one line

The volume of a cylinder is:

A worked example

Worked example. Take a cylinder with a diameter of 18 in (so a radius of 9 in) and a height of 24 in. The base area is π × 9² = 254.47 in², and multiplying by the height gives a volume of about 26.4 US gallons (6,107 in³ · 100.1 litres).

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

Measure the inside diameter of a tank, not the outside — the wall does not hold liquid. 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:

How much does a full tank weigh?

Water is about 8.34 lb per US gallon, or 1 kg per litre. Tick estimate weight, choose water, and the calculator multiplies the volume by density to show the load a full tank puts on its stand or floor.

How do I read a tank that is only part full?

For an upright tank, enter the current liquid height instead of the full height. For a tank lying on its side, use the horizontal-tank mode, which turns a dip depth into gallons using the correct segment maths.

Is the answer US or Imperial?

Both are shown at once. In the United States use US gallons; most other English-speaking countries use the larger Imperial gallon. Mixing the two is the single most common tank-sizing error.

How many litres is that in metric?

Every gallons result on this page is shown next to its litre value in the breakdown, because 1 US gallon is about 3.785 litres and 1 Imperial gallon is about 4.546 litres. You can hand the same figure to anyone regardless of which system they use.

Common mistakes to avoid

The mistakes that cost the most are unit mistakes. Reading a US figure as Imperial, or the reverse, is a 20% error before you start. Measuring the outside of a tank instead of the inside quietly overstates capacity, and forgetting the headspace at the top overstates it again. Measure inside, confirm which gallon, and treat the result as a full-to-the-brim maximum.

Getting the number in the unit you need

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.

What to work out next

Once you have your answer you may also want to work in tank capacity litres & liters cubic feet. These related calculators pick up where this one leaves off:

When this comes in handy

A few of the jobs it gets used for:

• Sizing a water storage or rainwater tank
• Working out fuel or oil drum capacity
• Estimating how many gallons a pool or trough holds
• Checking a well or cistern volume

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