How many fish in a 5 gallon tank?

Short answer: roughly 5 small, slim fish (like neon tetras or rasboras) in a well-filtered 5 gallon tank — far fewer if they grow larger. Good options: Pea puffer, Cherry shrimp.

Tested stocking ideas

Single pea puffer

1 × Pea puffer

Stocking level about 7% · heater 72–82 °F · all pairs compatible · open in calculator

Cherry shrimp colony

10 × Cherry shrimp, 1 × Nerite snail

Stocking level about 11% · heater 72–77 °F · all pairs compatible · open in calculator

Species that fit a 5 gallon tank

Maximum shown is for that species alone, at about 85% of a conservative stocking level. When mixing species, use the stocking calculator.

Species	How many (alone)	Note
Cherry shrimp	up to 91	groups of 10+
Nerite snail	up to 60
Pea puffer	up to 11

How we calculate it

We count each fish in "units": one slim 5 cm (2 inch) fish = 1 unit, and a well-filtered tank holds about 1 unit per US gallon. Units scale with (adult length ÷ 5 cm)^1.5 × a body-mass factor, so a 15 cm angelfish counts as about 8 units, not 3. Species are excluded if their recommended minimum tank is larger than 5 gallons.

Other sizes: 10 gallon · 20 gallon · 29 gallon · 40 gallon · 55 gallon · 75 gallon

FAQ

How many fish can I put in a 5 gallon tank?

It depends on the species. As a conservative guide, a 5 gallon tank holds about 5 small (2 inch) slim fish, far fewer large or heavy-bodied fish. The table above lists the maximum for each suitable species kept on its own.

Is the 1 inch per gallon rule accurate?

Only for small, slim fish. Waste output grows much faster than length, so a 6 inch fish produces far more waste than three 2 inch fish. We scale by body size and body shape instead.

Note: Compatibility depends on individual temperament, tank size, decor and how fish are introduced. Our verdicts use conservative rules applied to published care data (see methodology). They are guidance, not a guarantee. Quarantine new fish and watch for chasing, torn fins or hiding.