Imperial and US customary (non-metric) unit of volume
If all the sides were 1 foot in length, the amount of fluid that can be put in the box would be a cubic foot.
A cubic foot is a measure of volume. It is the amount of liquid that can be fit into a box 1 footdeep, one foot wide, and one foot in length. A cubic foot can be written ft3. It is used in the United States, and partially in Canada, and the United Kingdom.