Okay, online conversion calculators and Skene's conversion tables tell me that one cubic foot of volume (12x12x12=1728 cubic inches) is equal to a little under 7.5 gallons of liquid.
I measured the dimensions of a gallon of water in one of your standard plastic buckets and it came to 9" diameter by 7.5" height in the approximate cylinder. Using Pi times R squared times height the cubic inches of a gallon are 3.14 X (4.5 x 4.5) x 7.5 = 477 cubic inches
1728 cubic inches (a cubic foot) divided by 477 cubic inches (my measured gallon) = 3.62 gallons per cubic foot... not 7.5
What gives? Did I miss multiplying by 2 somewhere..or something else? I don't see where.
3.62 seems about right to my eye: four one quart containers of milk fitted side by side in a square looks to be a little less than a cubic foot.