Sena, that's just for fancy goldfish. For comets or commons, the type you win at carnivals, it's a 55gal as a bare minimum for one, with a 20 gallon minimum for each additional fish. I am setting up a 125 gallon pond, and keeping just 4 in there would be pushing it.
Turquioce: unless you have the space for a pond, I wouldn't suggest keeping any. If you keep one, you really need to keep 3, because they are group animals. 3 goldfish means *at least* a 90 gallon tank or pond with heavy filtration. That's a massive investment.