Free tool
Aquarium Volume & Stocking Calculator
Enter your tank's dimensions for its real water volume, filter target and a conservative stocking plan.
Actual water volume
58litres
12.8 imperial gallons · 65 L brim-full
- Floor area
- 18 cm²
- Filter flow to aim for
- ~292 L/hour
A workable stocking for this tank
- 8–10 small shoaling fish. Neon tetra, harlequin rasbora or ember tetra. One species, not three.
- + 6 corydoras. Pygmy or panda corydoras. They need floor area and a soft substrate.
- + 1 centrepiece. A dwarf gourami or honey gourami uses the upper level.
Deliberately conservative, and based on adult size rather than the size fish are sold at. A heavily planted tank with strong filtration carries more; a bare tank with a small internal filter carries less. Add fish in small groups over weeks, never all at once.
Why your tank holds less than it says on the box
A tank sold as 60 litres is measured brim-full and empty. Once you’ve added substrate, hardscape and left the two or three centimetres below the rim that stop it overflowing, you’re typically down around ten percent. On a nano tank that difference matters, because the smaller the volume, the faster everything in it swings.
The calculator takes that ten percent off automatically, which is why the figure it gives is lower than the number on the label. Dose medications and treatments against the real volume, not the advertised one.
Volume isn’t the only limit
Four separate things cap how many fish a tank can hold, and the lowest one wins: the adult size of the species, the biological capacity of the filter, the floor area and swimming length available, and the shoal sizes each species needs to be comfortable. A shoaling species doesn’t take one slot in a stocking plan. It takes six.
That last point catches people out more than any arithmetic. Six neon tetras in a tank is a stocking decision, not one fish’s worth of waste.
Stock on adult size, always
Common plecos are sold at 5 cm and reach 45. Common goldfish reach 25–30 cm and live for twenty years. Bala sharks hit 30 cm and shoal. Fish do not grow to the size of the tank: in a tank that’s too small, skeletal growth stunts while the internal organs keep developing, which shortens the fish’s life.
Before adding anything, the tank needs to be cycled. Our fishless cycling guide walks through the three to six week process, and the stocking guide covers the four caps in more detail.
Common questions
Multiply length by width by height in centimetres and divide by 1,000 for litres. Then take off around 10 percent for substrate, decor and the gap below the rim, which gives the volume of water actually in the tank.
No. Waste output scales with body mass rather than length, so one 10 cm fish produces far more than ten 1 cm fish. The rule also ignores swimming space, tank shape and shoaling needs.
Aim for a turnover of four to six times the tank's water volume per hour for a community tank, and more for messy fish like goldfish or larger cichlids. Biological media capacity matters as much as raw flow rate.
A tall 60-litre column and a long 60-litre tank hold the same water and suit different fish entirely. Active swimmers need length, bottom dwellers need floor area, and angelfish need height.
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