What Do Pets Need
Your answer

What does a goldfish need?

One adult goldfish needs a filtered tank of at least 100 liters (26.4 gallons) by OATA’s count, plus 50 liters for each one after.

How many

Your tank

Your tank against each minimum

What to get

What to get

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Tank shape for a full grown goldfish

RSPCA Australia sizes the tank by the fish as well as by volume: at least 4 times the adult’s body length long, 2 times wide and 3 times high. For the adult sizes OATA gives, that comes to the sizes below.

RSPCA Australia’s minimum tank shape, worked out for OATA’s adult sizes
GoldfishAdult lengthTank (L x W x H)In inchesSize from
Fancy goldfish20 cm (7.9 in)80 x 40 x 60 cm31.5 x 15.7 x 23.6 inOATA: unlikely to grow larger than 20 cm
Goldfish in an aquarium25 cm (9.8 in)100 x 50 x 75 cm39.4 x 19.7 x 29.5 inOATA: up to 25 cm is more common

Compare with the fish tank sizes chart.

Common, comet or fancy

Goldfish have been reported at 40 cm and more, though in an aquarium up to 25 cm is more common (OATA). Fancy goldfish are unlikely to pass 20 cm.

OATA advises against keeping common or comet goldfish with fancy ones: they swim faster and often out-compete the fancies for food.

Common questions

How many goldfish can go in a 55 gallon tank?

Three adults, by both OATA's rule of 100 liters for the first and 50 for each extra, and RSPCA's 60 liters each. A 55 gallon tank holds about 208 liters. RSPCA's other rule, 2 liters of water per 0.5 cm of goldfish, gives 100 liters for each goldfish at OATA's 25 cm adult size, so two.

Can goldfish live with other fish?

RSPCA Australia says goldfish can live with most community fish, as long as the other fish are larger than the goldfish's mouth.

Keep going

How many fish can go in my tank?What size aquarium filter?Fish tank sizes chartFish and shrimp

Where we get our information from

Care and tank sizes come from OATA, RSPCA and RSPCA Australia, and filter flow from Aqueon. Checked against published data from RSPCA, OATA, NIST, RSPCA Australia and Aqueon.

See all 7 sources
  • NIST Handbook 44 (2024), Appendix C: 1 US gallon = 231 cubic inches = 3.785 liters (PDF)
  • RSPCA, Ornamental fish: Environment (“Choosing an aquarium”)
  • RSPCA, Ornamental fish: Diet
  • OATA, How to care for fancy goldfish, January 2023 (PDF)
  • OATA, How to care for goldfish in aquaria, January 2023 (PDF)
  • RSPCA Australia knowledgebase, How should I care for my goldfish?
  • Aqueon, “How to Choose the Best Filter for You and Your Tank” (maker article)

General care guidance from animal welfare charities, vets and makers' published sizes. It isn't veterinary advice: if your pet seems unwell or has eaten something it shouldn't, call your vet.