Aquarium Size Calculator

Calculate the minimum aquarium size for your fish. Get tank recommendations, filter GPH, and heater wattage based on fish count, size, and type.

Inputs

Number of Fish

Average Fish Size

inches

Fish Type

Live Plants

Tab to move between fields

Results

Minimum Gallons

20 gallons

≈ 4 buckets

Recommended25 gallons

Standard Tank29 gallon — 30×12×18 in

Filter Rating100 GPH

Heater125 watts

How to Use This Calculator

Enter Number of Fish, Average Fish Size, and Fish Type.
Set Tropical (1 gal/inch), Goldfish (2 gal/inch), and Cichlids (2 gal/inch).
Adjust Marine (5 gal/inch), Live Plants as needed.
Review the Minimum Gallons (gallons) result.
Use Recommended (gallons) and Standard Tank to inform your decision.

How the result changes with Number of Fish

Number of Fish	Minimum Gallons
11	22 gallons
36	72 gallons
65	130 gallons
90	180 gallons

What each input means

Number of Fish: Number of fish in the tank.
Average Fish Size: Average fish size in inches.
Fish Type: Type of fish.

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Number of Fish = 10, Average Fish Size = 2, Fish Type = 0, Live Plants = 0 = 4 input(s) provided
Calculate Minimum Gallons
Minimum Gallons
20 = 20
Calculate Recommended
Recommended
25 = 25
Calculate Standard Tank
Standard Tank = Record<number
29 gallon — 30×12×18 in = 29 gallon — 30×12×18 in

Engine last updated July 28, 2026. Checked against 2 independently-derived tests — how we verify calculators.

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