It really depends on you! They can live in anything from 1-1.5 gals up to however big you want. My one Betta, Sparks, was VERY happy in his 1 gallon cube. But my guy Dragonfly was tail biting in his 2 gallon tank, so I upgraded him to a 5 gallon and now he is way more active and not tail biting! :-DI have my betta fish Flame in a 2 gallon bowl, heated, and he seems happy. I was curious what's the max Size of tank you should keep a betta in? I want flame to be the happiest he can be and I will upgrade to a bigger tank if it would make a difference.