A good rule of thumb is to start with aminimumtanksize of 20 gallons for 1-2goldfish, adding 10 gallons per additionalgoldfish. Opting for a largertankcan provide more stable water conditions, allow for morefishto be kept, give thefishmore swimmingspace...
Goldfishtanksize calculations. It’s not uncommon to see 100 litres, or thereabouts, quoted as theminimumfor onegoldfish, with varying amounts of additional litres for additionalfish.
Theminimumtanksizeforgoldfishshould be 20 US gallons / 75 UK Litres for the firstfish. Add 10 gallons (37L) to thetank’s capacity for every additionalgoldfish.Our suggested startertankforGoldfish. Glass or Acrylic? Largerfishtanksare usually made from glass.

The recommended commongoldfishtanksize is at least 20 gallons perfish. Unlike some fancy varieties, the commongoldfishis a slim-bodiedgoldfishthat will take up lesstankspacein bulk but will grow longer than most fancygoldfish.
MinimumTankSizeforGoldfish. Nothing beats the joy of admiring your mesmerizinggoldfishin their beautifully designedtank.Address these factors when choosing theminimumtanksizeforgoldfish:Fishtype: Either common or fancy, with differentspacerequirements.

Goldfishare social, messyfishthat require a significant amount ofspace. Therefore, it is important to house them in large aquariums. A 55-gallon aquarium can comfortably accommodate around three fancygoldfish(provided that it has enough filtration).
The absoluteminimumtanksize fortwogoldfishis 30 gallons. This allows for 20 gallons for the firstgoldfishand an additional 10 gallons for thesecond.
Goldfishprefer largertankswith adequate room for swimming. Whether you own a commongoldfishor slim-bodiedfish, thesefishwill thank you for the extraspacein a largertank. This article explains the besttanksizeforgoldfishand what to include in agoldfishtank.