Others have already addressed the issue of calculating fuel weight, but I'd like to take a moment to discuss what you wrote in a comment to the question.
85,000lbs of a liquid would seem to take up a lot of space and my friend and I were trying to figure out where all this liquid goes.
One of the beauties of the metric system is that one liter is exactly equal to one cubic decimeter (the latter, of course, being a cube of 10x10x10 cm; in US terms, that's a shade under 4x4x4 inches). A liter, like a cubic decimeter, is a unit of volume, rather than a unit of mass.
320,000 liters thus corresponds directly to 320,000 dm3. In a more usable unit, this is 320 m3 because 1 m3 = 1,000 dm3.
Looking at Wikipedia, the wing area of the A380 is given as 845 m2.
If the entire wing area can be used for fuel tanks, which is not the case, and there are only fuel tanks in the wings, which is not the case, this means that the average height of the fuel tanks in the wings would need to be equal to 320 m3 divided by 845 m2, or about 0.38 meters; a little thicker than the long side of a piece of A4 or Letter paper. I haven't flown in an A380 recently, but I suspect that the wings are thicker than this. The fuel also isn't kept only in the wings; while I don't know about the A380's configuration specifically, it's common for large aircraft to have both wing tanks, a center tank within the fuselage, and a trim tank farther back in the fuselage.
Bottom line here, there's plenty of room for that amount of fuel.