54 gallons is just called 54 gallons. There isn't a specific name for that quantity of liquid.

However, you might be thinking of something like:

* A barrel: A barrel is a unit of volume used for liquids, typically holding around 31 gallons.

* A hogshead: A hogshead is an older unit of volume, typically holding about 63 gallons.

If you are trying to figure out a better way to describe 54 gallons for a specific purpose, let me know what you're using it for, and I might be able to help you find a more suitable term!