There are two types of mechanical freezers, upright and chest freezers. Upright freezers have side-loading doors and chest freezers have top loading doors.  Also, there are liquid nitrogen freezers that have top loading lids.  All of these freezers are designed for racks that store 5 ¼” x 5 ¼” x 2” standard boxes.  For example, the interior dimensions of a 21 cubic foot upright freezer is 50.5” high x 24.25” front-back x 28.5” wide and there are five 9 5/8” high shelves.  Five Custom Biogenic Systems URO442 racks will fit on each shelf for a total capacity of twenty-five URO442 racks.  The dimensions of the URO442 rack are 9 ¼” high x 22 1/8” front-back x 5 ½” wide, and it holds sixteen boxes.  If a standard box with an 81-cell divider is used, each box will hold 81 vials.  The total vial capacity in the 21 cubic foot freezer is 32,400 vials (18 vials x 16 boxes x 25 racks).

If a scientist selected a 100-cell hinged top plastic storage box for storing vials in the 21 cubic foot freezer, the total vial capacity would only be 24,000.  This is because the rack that would fit into the 21 cubic foot freezer is a UHT34 rack.  Only four UHT34 racks fit on each shelf – twenty racks total.  Also, the UHT34 holds twelve100-cell hinged top plastic boxes.  Thus, the total vial capacity in the 21 cubic foot freezer is 24,000 vials (100 vials x 12 boxes x 20 racks).

Standard boxes (5 ¼” x 5 ¼” x 2”) have been used since the 1960’s, the start of -86º C mechanical freezers and liquid nitrogen freezers.  Racks and boxes were created at about the same time for storage in these freezers.  Glass vials were originally used and plastic vials came soon afterward.  The freezers of the 1960’s were designed to store as many vials as possible.  Storage racks were created to store boxes and to fit into the freezer shelves.  Freezer manufacturers designed their equipment to provide the most efficient capacity of standard box storage.

Does any rack fit any freezer?  Possibly, but it may not be efficient storage.  Measure your rack dimensions and your freezer dimensions to get the best use of rack storage.