There's no official standard for how big a "mini" fridge can be, but most are simultaneously shorter, slimmer, and narrower than full-size models, with 5-ish cubic feet or less of interior space.

[Compact Size and Large Capacity] This apartment size refrigerator has a small footprint and large storage space. Measuring 16.7*17.5*40.1 inches, it has a total capacity of 4.0 cu. ft. including ...