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.
Why this result
The minimum tank comes from the species' welfare standard; the recommended size scales up when your group exceeds the species' standard school size.
Assumptions
- Sizes are US gallons.
- Aquascape layout and other tank mates are not counted in this figure.
- Algorithm v1.1 — schooling species need room for the full group.
Algorithm v1.1 · reviewed
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.
Explore More
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 15–20 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: