For Shale, the swell factor is around 70%.
Swell Factor = loose wt / bank wt per unit volume.
So you may get loose wight around 2500 lbs per cu. yrd and Bank weight near 3500 lbs per cu. yrd.
If however, you need to approxiamte percent swell it is near 40%.
%Swell = [ (bank unit wt/loose unit wt) - 1 ]x100
or in our example [(3500/2500 - 1]x100 = 40%