The CDC and VFC set out guidelines that pertain to the size your vaccine refrigerator should be. The size of the appliance has to directly correspond with the amount of vaccines doses that get administered each month.
The reason this is recommended is to prevent refrigerators that store vaccines from getting over crowded. If you try and cram too many vaccine boxes into and stack them on top of each other this can hinder the proper airflow inside the fridge which will cause temperature variations inside throughout the appliance.
The following calculator will help you find the right size vaccine fridge for your needs. You just need to enter the amount of vaccines you store that you administer for public funded programs such as VFC, Medicare, and Medicate as well as the amount of vaccines you purchase and administer for patients with private insurance: