Stocking
Find out how many fish your tank can safely hold. Bioload-based stocking levels for any aquarium size and species mix.
Estimate how many fish your tank can hold. Set your volume, add species, and watch the stocking level — bioload-weighted, not the outdated “one inch per gallon” rule.
Room for roughly 3 more small community fish.
Next step
Found your mix? Find an aquarium store near you that carries these species and the gear to support them.
Find stores near meQuick answer
Match your tank's real water volume to the adult size and bioload of each species, not the outdated one-inch-per-gallon rule. A 10-gallon holds about 6-8 nano fish; a 29-gallon holds a small community plus a centerpiece fish.
Quick reference
How to use
Stocking is about bioload, not a length-per-gallon rule. This aquarium stocking calculator weighs each species' adult size and waste output against your tank's real water volume to estimate how many fish you can safely keep — and how many fish fit in a 10, 20, 29, or 55 gallon tank.
Start with your tank's true water volume in gallons. If you only know the dimensions, run the tank volume calculator first, then subtract 10-15% for substrate and decorations.
Pick each species and quantity. The calculator pulls each fish's adult size, bioload, and minimum tank size — not the size it is in the store tank today.
The result shows your stocking percentage. Stay at or under 100%, and treat anything over ~85% as a signal to upgrade filtration and increase water changes.
Add fish a few at a time over several weeks so your biological filter can keep pace. A fully stocked new tank crashes; a slowly stocked one stabilizes.
Common sizes
Pro tips
Quick facts
Pitfalls
Learn from others' errors to ensure accurate calculations and healthy aquatic life.
Why it matters — Wildly overstocked tanks — it ignores body mass, waste output, and adult size
Do this instead — Use a bioload- and volume-based estimate and respect each species' minimum tank size
Why it matters — Ammonia spikes the young filter can't process, killing fish
Do this instead — Add fish gradually over several weeks so beneficial bacteria can keep up
Why it matters — A cute 1-inch fish becomes a 12-inch tank-buster
Do this instead — Always plan stocking around full adult size, not the size in the store
Why it matters — Stressed, nippy, hiding fish when kept in groups that are too small
Do this instead — Keep schooling species in groups of 6+ and count every one toward your stocking total
Source locally
To stock your tank, you'll want:
Products
tropical fish · aquarium filters · test kits · water conditioners
Services
fish ordering · stocking consultation
Reference
Next up
Double-check the fish get along and the tank's the right size:
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