Aquarium Tank Volume Calculator

What this does

So you want to know how much water your tank actually holds. This works it out. Pick the tank shape, pop in the dimensions, and it gives you the volume in both gallons and litres. It covers the three common shapes, a standard rectangle, a bow front, and a cylinder, so it suits most tanks you are likely to have.

How to use it

1. Choose the tank shape. The boxes change to suit it, so a cylinder asks for a diameter, and a bow front asks for a full width.
2. Enter each dimension, and pick the unit for each.
3. Tap Estimate to see the volume in gallons and litres.

You can mix units if you need to, since each measurement has its own unit selector.

How it works

It is geometry under the hood, with every measurement converted to inches first. For a rectangle, it is simply:

volume = length × width × height

For a cylinder, it uses the circle area times the height, where the radius is half the diameter:

volume = π × radius² × height

A bow front is handled as the rectangular body plus the curved front, which it approximates as a half ellipse bulging out. Once it has the volume in cubic inches, it converts using the fact that one US gallon is 231 cubic inches, then turns gallons into litres. It all runs on your device.

Why volume matters

Volume is the number nearly everything else hangs off. It guides how many fish a tank can sensibly hold, though the old one inch of fish per gallon idea is rough at best, since real stocking depends far more on the species, their adult size, and your filtration. It also helps you size a filter and heater, and work out water changes and doses of treatments. One thing to keep in mind, this is the tank's full capacity, and the actual water volume is a little less once you account for substrate, rocks, and not filling right to the brim. And do not forget the weight, because all that water is heavier than it looks.

Questions people ask