The minimum specified volume of a 48G cylinder is 139 ft3
139 ft3 x 62.37 lb/ft3 = 8,670 LB of water
Nameplate water weight must exceed 8,670 LB, then
95% (139 x 203.3) = 26,840 LB UF6
This is the published fill limit
For each type of cylinder, a fill limit is calculated and published based on the minimum specified volume and allowing for a 5% void space when heated to 250°F.