A quick way to see how heavily stocked your tank is. Enter your volume, add your fish with their adult length, and it works out an approximate stocking percentage. It is a guide to help you plan, not gospel; the honest test is always your water and your fish. For a more detailed model with a species list and compatibility checks, use the fuller stocking calculator.
Use your real water volume, not the box's rated size. Rock, substrate and the gap below the rim usually knock off 10 to 15%. The volume calculator works it out from your dimensions.
The old "one inch of fish per gallon" rule is a poor guide, because a single large fish makes far more waste than the same length split across many small ones, and it ignores how much oxygen and gas exchange a tank's surface can support. This calculator instead adds up the combined adult body length of all your fish, then compares it against your water volume with a surface-area factor, so a tall, deep tank is treated a little more cautiously than a long, shallow one of the same volume. It targets a sensible community-tank density and shades from lightly stocked, through healthy, to overstocked.
Whatever number it gives, the real limit is your biological filtration and your maintenance. A tank with mature, well fed filter media and regular water changes carries more than a fresh one. If the water goes cloudy or nitrate climbs week on week, you are overstocked no matter what any calculator says. Read up on how many fish you can keep, size the filter with choosing an aquarium filter, and keep an eye on your water parameters.
As a rough starting point, allow around 1 cm of adult fish length per 2 litres of actual water for an averagely stocked community with good filtration. This calculator applies a surface-area factor so deep tanks are treated more cautiously. Treat it as a guide, then watch the tank rather than the number.
Not really. One 30 cm fish is nothing like ten 3 cm fish for waste output, and the rule ignores body mass and surface gas exchange. Combined adult body length scaled by surface area, as used here, is a better guide, but it is still only an estimate.
Bioload is the total waste your fish produce, mostly ammonia, that your filter bacteria have to process. More fish, bigger fish and heavier feeding all raise it. A stocking calculator estimates bioload from fish size; the true limit is your biological filtration and your water changes.
A guide only, not a guarantee. It sums the adult body length of your fish and compares it against your water volume with a surface-area adjustment, aiming at a typical community density of roughly 1 cm of fish per 2 litres at good filtration. It says nothing about compatibility, temperament, group sizes or minimum tank sizes; for those, and a metabolic-weight model, use the fuller stocking calculator. The honest gauge is your own water: if it goes cloudy or nitrate rises, stop adding fish.