Fish Tank Size Calculator
Pick a species and how many you plan to keep —get the minimum tank, the recommended tank for a healthy group, and standard tank sizes that fit, straight from our fish database.
- Minimum tank size
- 5 gallons
- Recommended tank size
- 60 gallons
- Suggested standard tanks
- 75 gallon (48 × 18 × 21") or 90 gallon (48 × 18 × 25")
- Schooling
- Betta (Siamese Fighting Fish) is fine alone or in pairs.
- Dimensions shown are external, in inches (L × W × H). Long variants trade height for swimming length.
- Run the Stocking Calculator to plan a full community around this species.
How It Works
Every species profile in our database carries a minimum tank size and a recommended tank size. The minimum is the floor below which welfare suffers; the recommended size allows natural behavior and stable water. For schooling species, the recommendation scales with your group size beyond a standard school. The calculator then matches your result against common standard tanks —with their actual dimensions —so you can walk into a store with a shortlist.
Formula
Minimum Tank = Species Minimum (from fish database)
Recommended Tank = Species Recommended × (Group Size ÷ Standard School)
Example
Planning 12 neon tetras: the species minimum is 10 gallons, and 12 fish is twice a standard school of 6 —so the recommendation scales from 15 to 30 gallons. The closest standard matches: a 29 gallon (30 × 12 × 18) or a 40 Breeder (36 × 18 × 16).
Important Limitations
- Recommendations are for a single-species group; mixed communities are planned in the Stocking Calculator.
- Standard tank dimensions are external and vary slightly by manufacturer.
FAQ
What size tank does my fish need?
It starts with adult size and swimming style. Neon tetras want a 10 gallon minimum and really shine in a 15–0 gallon school tank; angelfish need 30 gallons minimum and a 55 to thrive. Select your species above for its specific numbers.
Does the number of fish change the tank size?
Yes, especially for schoolers. A group of 12 neon tetras needs roughly double the footprint of a standard school of 6 —the calculator scales the recommendation with your group size.
Is a taller tank better than a longer one?
For most fish, no. Swimming room (length and width) matters far more than height —that is why a 20 gallon Long suits danios better than a standard 20. Height mainly matters for tall-bodied fish like angelfish.
What are the most common standard tank sizes?
10 gallon (20 × 10 × 12 in), 20 gallon (24 × 12 × 16), 20 Long (30 × 12 × 12), 29 gallon (30 × 12 × 18), 40 Breeder (36 × 18 × 16), 55 gallon (48 × 13 × 21), and 75 gallon (48 × 18 × 21) are the workhorses of the hobby.
Should I buy the minimum tank size?
Treat the minimum as a floor, not a target. Bigger tanks are more chemically stable, forgive maintenance lapses, and open up stocking options later. If you are between sizes, size up.
Sources
- Aquarium Forge fish database —reviewed species care standards
- Standard aquarium dimensions —industry common sizes
Last reviewed: