Is my fishtank overcrowded?

Hi, i have a tank which i have 16 litres of water in it. I think that works out to be 3.5 gallons. I have 3 goldfish and 2 guppies in the tank with a filter that cycles 500L water per hour. The tank seems extremely clean and the fish seem happy but id like to know, if i have more fish in the tank than im supposed to. The goldfish are pretty small, except for the latest one which is about 2inches or smaller, and the guppies are small as well( the male is about 1/2 inch and the female is about an inch, mabey smaller) K well thanks for your help :)