About 2–3 — based on adult size, bioload, and real water volume.

In a 55-gallon tank you can comfortably keep about 2–3 goldfish (fancy), on their own with good filtration and regular water changes. Add fewer if you're mixing in other species.
An adult goldfish (fancy) reaches about 8.0" and has a heavy bioload. Working from real water volume and waste output (not the old one-inch-per-gallon myth), a 55-gallon tank supports roughly 2–3 of them. They need 65–75°F water at pH 7–8.
Build your exact stocking with the calculator → Full goldfish (fancy) care guide →
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