How many fully grown goldfish can go in a 40 gallon tank?

Goldfish are popular aquarium fish, but they can grow quite large and require a lot of space. A single adult goldfish needs at least 20 gallons of water, so a 40 gallon tank could comfortably house two adult goldfish. However, it is important to note that goldfish produce a lot of waste, so it is recommended to keep only two or three goldfish in a 40 gallon tank to ensure the water quality remains healthy. Additionally, goldfish are social fish and prefer to live in groups, so it is best to keep at least two goldfish together.