Tank Volume Calculator

What the tank volume calculator does

A cylindrical tank holds more, or less, than people guess, and the figure you need is rarely the one written on the side. This works it out. You give it the diameter and height, and it returns the full volume in several units, and if you add how high the liquid sits, how much is actually in it.

It is built for the round tank, the most common kind, and it speaks every liquid unit you are likely to need. Below is how it works.

How to use it

1. Enter the height and diameter of the tank, each with its unit.
2. Add the filled height if you want to know the current contents, the depth the liquid reaches.
3. Press Calculate for the volume and capacity, or Reset to clear it.

How the volume is worked out

A cylinder's volume is the area of its circular end times its height. The end is a circle, so its area is pi times the radius squared, and the radius is half the diameter:

Volume = π × radius² × height

The calculator converts the measurements to meters, works out the volume, then expresses it as cubic meters, cubic feet, litres, US and UK gallons, and barrels, so whichever unit your trade uses is to hand.

The liquid units, including barrels

The same volume reads as very different numbers depending on the unit, which is why the calculator shows the lot. Litres and cubic meters suit most uses, but gallons come in two sizes that catch people out: a US gallon and a UK gallon are not the same, the UK one being the larger, so it matters which a figure is quoted in.

The barrel, marked BBL, is the one people meet least. It is the oil barrel, a petroleum-industry unit of 42 US gallons, or about 159 litres. So if you are dealing with fuel or oil storage and a figure comes in barrels, that is what it means, and the calculator gives it alongside the rest.

Working out a partial fill

The filled height turns the calculator from a tank-size tool into a contents gauge. Give it the depth the liquid reaches and it works out that smaller volume the same way, and tells you what fraction of the tank is full as a percentage.

This works for a tank standing upright, where the liquid forms a shorter cylinder of the same diameter. So if you can measure or read the level, you can turn it into litres or gallons in the tank, which is more use day to day than the full capacity alone.

A worked example: a 2 by 3 m tank

Say the tank is 2 meters across and 3 meters tall.

The radius is 1 meter, so the volume is π × 1² × 3, which is about 9.42 cubic meters. That is roughly 9,420 litres, or about 2,490 US gallons. Filled to 1.5 meters, half its height, it holds half that, since the diameter does not change up the tank.

So a tank that sounds modest in meters turns out to hold a couple of thousand gallons, which is the point of running the numbers.

Questions people ask

How do I calculate the volume of a cylindrical tank?

Multiply pi by the radius squared by the height. For a tank 2 meters across and 3 meters tall, that is about 9.42 cubic meters, or roughly 9,420 litres.

How many gallons does my tank hold?

Work out the volume and convert. The calculator shows both US and UK gallons, which differ, so check which one you need.

What is a barrel (BBL)?

The oil barrel, a petroleum unit of 42 US gallons, about 159 litres. The calculator shows it for fuel and oil storage.

How do I find how much is in a part-full tank?

Enter the height the liquid reaches as the filled height. For an upright tank the calculator works out that partial volume and the percentage full.

References

A quick note on the numbers. The volume is plain geometry, pi times the radius squared times the height. The conversions between cubic meters, litres, US and UK gallons, and the 42 gallon oil barrel follow the US National Institute of Standards and Technology guide.

1. National Institute of Standards and Technology (NIST), Special Publication 811, Guide for the Use of the International System of Units (SI). https://www.nist.gov/pml/special-publication-811