I would hope that the manufacturers/retailers would be able to tell you the dry weight per cubic foot. The Southdown I bought was quite wet from condensation and weighed more than the 50 pounds stated on the bag.
For instance, on the Carib Sea web site I found the following:
"To compute the amount of aragonite needed for your set-up, use the following equation: length of tank x width of tank x bed depth desired, divide the answer by 1,728, then multiply x 70. This is the poundage needed. "
Using that calculation for my tank (72 * 18 * 5" dsb
) yields 262.5 pounds or jsut over 5 bags of Southdown (SD being the same as Carib Sea aragonite sand).
I used 6 bags and 40 pounds of LS
and have a 5"-7"+ dsb