Assuming the same as water (which its not, but its a close guess), 1 cu ft of water = 7.5 gallons. Bleach is "heavier", density wise, but again a close enough guess I think.
The base of the LQ is 15"x15", which translates into needing 7.75" of height to make the 15x15 base take up 1 cu ft. So...