Measure the space.
Know the volume.
Inside measurements. Filled water height. Gallons with their meaning attached.
Your tank, from the inside.
Changes update the result as you type. No fish capacity or stocking combination is inferred.
60 × 30 × 30 cm ÷ 1,000 = 54 liters.
Capacity and working water
are different numbers.
The drawing describes the measured space. Substrate, rocks, wood and equipment reduce the water that actually occupies it. The calculator does not deduct them or estimate how much space your fish need.
Use a measured working volume when a precise amount matters. Do not turn the result into a fish-per-gallon rule.
Plan for the adult fishWhich gallon does a tank label mean?
A US liquid gallon is 3.785411784 liters. An Imperial gallon is 4.54609 liters. A tank marketed as 20 gallons is not enough information to establish its inside dimensions or working water volume.
Inches convert to centimeters using exactly 2.54 centimeters per inch. A cylinder uses its internal diameter; the radius is half that value. Bow-fronts and irregular shapes need a different measurement method.
NIST volume units ↗A quantity is a starting point.
Plan the substrate separately, calculate a chosen water-change amount, or keep a dated care record.