Neon tetras get to an average size of one and a half inches (4 cm) in length. Wild neon tetras grow larger than the ones in home aquariums.
Wild neon tetras can grow to a maximum of two and a half inches (6 cm) in length, while aquarium neon tetras usually don’t get bigger than one and a half inches (4 cm).
Even though these fish are small, be sure to give them enough space. Neon tetras should have at least a 20-gallon tank, so that a school of 10–13 fish can live comfortably.