Fish Tank Sizes

How many fish in a 5 gallon tank?

One betta, or a small school of the tiniest fish.

A 5 gallon tank is 16 inches long and 8 wide. That suits one betta or a school of 6 to 8 very small fish.

Stockings that work in a 5 gallon tank

Each mix has been run through the stocking calculator and comes out with no problems or warnings.

  • One betta

    1 × Betta. This tank is under the recommended minimum for Betta (a 18 x 12 in footprint).

    37% stocked
  • A small school of ember tetras

    8 × Ember tetra. This tank is under the recommended minimum for Ember tetra (a 18 x 12 in footprint).

    85% stocked
  • A few Endler's livebearers

    4 × Endler's livebearer. This tank is under the recommended minimum for Endler's livebearer (a 18 x 12 in footprint).

    53% stocked
  • A tiny school of chili rasboras

    8 × Chili rasbora. This tank is under the recommended minimum for Chili rasbora (a 18 x 12 in footprint).

    85% stocked

Try your own fish

Neon tetras schooling above corydoras catfish in a planted tank

Why not one inch of fish per gallon

That old rule says to allow one inch of adult fish per gallon. It is easy to remember and works well for small, slim fish like tetras and rasboras.

It breaks down for bigger and messier fish. A fish twice as long weighs several times as much, and goldfish and plecos make far more waste than their length suggests. Our calculator keeps the inch rule for fish under three inches and counts larger fish for more.

Both the volume and the footprint are small here, so the list of fish that really suit it is short. The ones on this page are the safe picks.

One kind of fish, nothing else

The most of each that suits a 5 gallon on its own.

Betta1 only *
Ember tetraup to 9 *
Guppyup to 3 *

* Fits by volume, but the footprint is under what Seriously Fish recommends for the species.

Before you add the last fish

  • Add fish slowly. A new tank needs weeks to grow the bacteria that process waste, so add a few fish at a time.
  • Count the minimum group. Schooling fish are stressed alone, so plan around the smallest group before the tank total.
  • Plan for adult size. Fish in the shop are usually young.
  • Match the filter. Look for one rated for 20 to 30 gallons per hour.

A full tank is not a target. One at 60 to 80% is easier to keep clean and gives fish room to settle.

Sizes and weight: 5 gallon tank dimensions.

Common questions

How many fish can live in a 5 gallon tank?

One betta, or a small school of the tiniest fish. The example mixes on this page come out between 37% and 85% stocked by our calculator, with no warnings.

How many ember tetras fit in a 5 gallon tank?

Up to 9 ember tetras in a 5 gallon with nothing else in it. Add other species and that number comes down.

Is one inch of fish per gallon a good rule?

It works for slim fish under about three inches, such as tetras and rasboras. It fails for larger or messier fish, because a fish twice as long has several times the body mass. Count big fish for more.

What size filter does a 5 gallon tank need?

One rated for 20 to 30 gallons per hour, which turns the water over four to six times an hour.

Gear for a 5 gallon tank

Searches on Amazon for the right size. Check the tank size or flow rating on the listing before you buy.

Heater, 25 WSized for a normal room.Filter, 20 to 30 gphA hang-on-back or sponge filter works.Stand, 16 x 8 in or largerMust support the whole bottom frame.Lid or hood, 16 x 8 inKeeps fish in and slows evaporation.Water test kitTracks ammonia, nitrite and nitrate.Water conditionerRemoves chlorine from tap water.

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