What this calculator does
Fish tank stocking works out roughly how many inches of fish a freshwater community tank can hold. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaCapacity (in of fish) ≈ tank size in gallons, the classic "1 inch of fish per gallon" community-tank rule
The inputs explained
| Field | What to enter |
|---|---|
| Tank size (US gal) | A number, measured in US gal. Starts at 20. |
| Fish lengths (comma-separated, inches) | A list of numbers, separated by commas or spaces. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with tank size
Every other input is held at the calculator’s starting values while tank size varies. Select any row to load that scenario into the calculator.
How the answer changes with tank size