It may surprise you
In all the years I worked selling appliances at THD, I learned that there is no conformity (by the government or anyone else) as to how cubic footage is to be measured for refrigerators/freezers. It's strictly based on what the manufacturer decides is "usable capacity". Things like hinges, brackets, or interior moldings may/may not affect the actual number. Most manufacturers will include an approximate capacity in the model number, but 17.8 cu. ft. may be shown as "18", for example.