Aquarium Stocking Calculator

Fish count from tank volume, species, and filtration.

Tank Volume (gallons)

Filter Capacity (GPH)

Tank Type

Tab to move between fields

Recommended Stock (inches)

Max Fish Inches (base rule)20

Max Fish Inches (filtration-adjusted)20

Est. Small Fish (2″ avg)7

Est. Medium Fish (3.5″ avg)4

Filter Turnover (x/hr)5

Filtration Adequacy (%)100

Type LabelFreshwater

How to Use This Calculator

Enter Tank Volume (gallons), Filter Capacity (GPH), and Tank Type.
Review the Recommended Stock (inches) result.
Use Max Fish Inches (base rule) and Max Fish Inches (filtration-adjusted) to inform your decision.

How the result changes with Tank Volume (gallons)

Recommended Stock (inches): Conservative recommended total fish inches based on tank and filtration.
Max Fish Inches (base rule): Maximum total inches of fish using the classic stocking rule.
Max Fish Inches (filtration-adjusted): Adjusted maximum based on your actual filter capacity.
Est. Small Fish (2″ avg): Approximate number of small community fish (tetras, rasboras).
Est. Medium Fish (3.5″ avg): Approximate number of medium fish (gouramis, small cichlids).
Filter Turnover (x/hr): How many times per hour your filter processes the full tank volume. Target: 4-6x.
Filtration Adequacy (%): How well your filter meets the recommended 5x turnover rate.

Identify Input Parameters
Tank Volume (gallons) = 20, Filter Capacity (GPH) = 100, Tank Type = 1 = 3 input(s) provided
Calculate Recommended Stock
Recommended Stock = adjustedMaxInches * 0.75
15 = 15
Calculate Max Fish Inches
Max Fish Inches = tankVolume * inchesPerGallon
20 = 20
Calculate Max Fish Inches
Max Fish Inches = maxTotalInches * filtrationMultiplier
20 = 20