Aquarium Stocking Level Calculator

Work out aquarium stocking level instantly with clear inputs, formula shown and shareable results.

About Aquarium Stocking Level Calculator

The classic rule allows about one centimetre of adult fish length per litre of water, so capacity is the volume divided by that rule and stocking is the current length against it. The rule is a rough guide because waste output scales with fish mass not length, so a single large fish loads a tank far more than several small ones of the same total length.

Formulas

Capacity

supported fish length = tank litres / centimetres per litre

Stocking level

stocking % = current fish length / supported length x 100

Worked example

With the default values below, Aquarium Stocking Level Calculator returns Stocking level of 50.00%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Tank volumeminimum 1 L: 120 L
Combined adult fish lengthminimum 0.1 cm: 60 cm
Stocking ruleminimum 0.1 cm per L: 1 cm per L

Results

Stocking level: 50.00%
Total fish length the tank supports: 120.0 cm
Fish length you could still add: 60.0 cm
Assessment: Within a comfortable range

Step by step

1Values used
2Capacity
3Stocking level
4Stocking level= 50.00
5Total fish length the tank supports= 120.0 cm
6Fish length you could still add= 60.0 cm
7Assessment= Within a comfortable range

Assumptions and limits

The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is the Aquarium Stocking Level figure worked out?

supported fish length = tank litres / centimetres per litre. The classic rule allows about one centimetre of adult fish length per litre of water, so capacity is the volume divided by that rule and stocking is the current length against it.

Why does this matter?

The rule is a rough guide because waste output scales with fish mass not length, so a single large fish loads a tank far more than several small ones of the same total length.

What do I need to enter?

Enter tank volume, combined adult fish length, stocking rule. The defaults shown are a realistic worked example — swap in your own figures to get a result you can use.