The most common aquarium size, according to research made in 2020, is the 20-gallon tank.
Nevertheless, these are the standard sizes per type of hobbyist.
10 gallon: this is a common aquarium size very popular for beginners. It's suitable for small fish species and can fit easily in most homes.
20 gallon: A bit larger common aquarium size. It provides more space for fish and allows for a greater variety of species.
29 gallon: Another intermediate common aquarium size, the 29-gallon tank is a good choice for those who want a moderately sized aquarium without committing to a large setup.
55 gallon: This is a larger common aquarium size that allows for a greater diversity of fish. It's a popular choice for hobbyists who want a more substantial aquarium.
75 gallon: A larger tank that provides even more space for fish and allows for more elaborate aquascaping or in cases where you want to have bigger fish or monster fish.