Find out how full your freshwater tank really is. Enter the tank volume, filter flow and the fish you keep or plan to buy, and get a stocking level percentage based on adult size and waste output, plus warnings for fish that need a bigger tank or a group.
Last updated:
Tank & filter
GPH
Gallons per hour on the filter box. 1 L/h = 0.264 GPH.
Fish
Over 45 common species are recognised. For others add the adult size: "Bumblebee goby, 6, 1.5" (or 4 cm).
Enter your values to see the result.
Advertisement
Advertisement
How to use the Aquarium Stocking Calculator
Enter the tank volume in gallons or liters and the filter's flow rate.
Choose the decor level and tick live plants if the tank is well planted.
List your fish, one species per line with the number of fish, e.g. "Neon tetra, 12".
Press Calculate stocking to see the stocking %, room left and any warnings.
Adjust the list to try out new fish before you buy them.
Example: a 29 gallon tank with normal decor (× 0.92 = 26.7 gal) and a 150 GPH filter (5.2× turnover, factor 1.15) has a capacity of 30.7 units. Twelve neon tetras (12 × 1.5 × 0.6 = 10.8), six corydoras (6 × 2.5 × 0.8 = 12) and one dwarf gourami (3.5 × 1 = 3.5) give 26.3 units, which is 86%: well to fully stocked.
Slim schooling fish 0.6, corydoras and small livebearers 0.8, average 1, cichlids, angelfish and bristlenose plecos 1.2–1.5, goldfish, common plecos and oscars 2, dwarf shrimp 0.2
Adult sizes and minimum tanks of popular fish
Fish
Adult size
Group
Minimum tank
Neon tetra
1.5 in (4 cm)
6+
10 gal (38 L)
Guppy
2 in (5 cm)
3+
10 gal
Betta
2.5 in (6 cm)
1 male
5 gal (19 L)
Corydoras
2.5 in (6 cm)
6+
20 gal (76 L)
Angelfish
6 in (15 cm)
1+
30 gal (114 L)
Fancy goldfish
7 in (18 cm)
1+
20 gal + 10 per extra fish
Common pleco
18 in (45 cm)
1
125 gal (475 L)
Stock a new tank slowly, a few fish every couple of weeks, so the filter bacteria can keep up. Test ammonia, nitrite and nitrate regularly.
Frequently asked questions
How many fish can I put in my tank?
A rough guide is about one inch of slim adult fish per gallon of water, with less for thick-bodied, messy fish like goldfish, plecos and cichlids. This calculator applies that rule to the real water volume, adds a waste factor per species and adjusts for filtration and plants.
Is the one inch per gallon rule accurate?
It is only a starting point. It works reasonably for small, slim fish such as tetras and rasboras, but a 10 inch fish produces far more waste than ten 1 inch fish. That is why large and heavy-bodied fish get a higher bioload factor and a minimum tank size check here.
What stocking percentage is good?
Around 50 to 85 percent is a comfortable level for most community tanks. 85 to 100 percent works with good maintenance. Above 100 percent the tank is overstocked: water quality drops quickly and more frequent water changes and stronger filtration are needed.
How strong should my aquarium filter be?
Most freshwater tanks do well with a filter that moves 4 to 6 times the tank volume per hour. A 29 gallon tank needs a filter rated at roughly 120 to 175 gallons per hour (GPH). Heavily stocked or goldfish tanks benefit from more.
Why does the calculator warn about schooling fish?
Fish like tetras, rasboras, corydoras and danios live in groups and become stressed, shy or nippy when kept alone or in pairs. Most should be kept in groups of at least 6.
Does it work for saltwater or ponds?
It is designed for freshwater aquariums. Marine tanks and ponds follow different rules because of oxygen levels, live rock and larger water volumes, so use the result only as a rough comparison there.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.