There are 7.35 cubic feet in a 55-gallon drum. This assumes that the gallon in question is a US gallon and that the volume of a liquid is being calculated.
The volume of 1 US liquid gallon is the equivalent of approximately 0.13 cubic feet. Therefore, the number of cubic feet in a 55-gallon drum is 0.13 multiplied by 55, which is equal to 7.35 cubic feet. Interestingly, the volume of 1 US dry gallon is greater than a liquid gallon, with 1 dry gallon having a volume of approximately 0.16 cubic feet. Using this conversion factor, a 55-dry-gallon drum would have a volume of 8.56 cubic feet.