Aquarium Stocking Calculator
Fill in the values and the answer updates as you type.
How the Aquarium Stocking Calculator works
The old rule allows one inch of adult fish per US gallon of water, so the fish count = gallons ÷ adult length in inches. It only suits slim fish under about 3 inches (7.5 cm). Bulky or messy fish such as goldfish, cichlids, and plecos need far more water per inch, and some species need a group or a large swim space. Treat the result as a ceiling, not a target, and research each species. Example: A 200 liter tank with 5 cm fish suggests up to 26 fish.
Inputs and results
The Aquarium Stocking Calculator takes 2 inputs and gives 3 results.
What you enter
- Water volume (liters) — starts at 200.
- Average adult fish length (cm) — starts at 5.
What you get
- Suggested number of fish
- Total fish length the tank can hold (cm)
- Total fish length the tank can hold (in)
Example: Aquarium Stocking Calculator with the starting values
With water volume 200 liters and average adult fish length 5 cm, the calculator returns:
| Suggested number of fish | 26 |
|---|---|
| Total fish length the tank can hold (cm) | 134 |
| Total fish length the tank can hold (in) | 52.8 |
Change any value above and the results update straight away.
Aquarium Stocking Calculator FAQ
How do I use the Aquarium Stocking Calculator?
Enter water volume and average adult fish length in the fields, then read suggested number of fish, total fish length the tank can hold (cm) and total fish length the tank can hold (in) in the result panel. The answer updates as you type, and you can press Calculate or Enter to refresh it. Use “Copy link” to share your exact numbers with someone else.
What does the Aquarium Stocking Calculator calculate?
Rough number of small fish a tank can hold using the inch-per-gallon rule. It returns suggested number of fish, total fish length the tank can hold (cm) and total fish length the tank can hold (in) from the 2 values you provide.
What values does the Aquarium Stocking Calculator start with?
It opens with water volume 200 liters and average adult fish length 5 cm so you can see a working result straight away. Replace them with your own numbers, or press Reset to return to these starting values.
Is the Aquarium Stocking Calculator free and private?
Yes. It is free, needs no account, and runs in your browser, so nothing you type is sent to or stored on our servers. See the Privacy Policy for details.
Can I rely on the Aquarium Stocking Calculator for medical or health decisions?
Treat the result as a well-rounded estimate. Real situations often have details a general calculator cannot know, so confirm medical or health decisions with a qualified professional. See the Disclaimer for more.