Aquarium Volume & Water Change Calculator
Calculate water volume for rectangular or cylindrical tanks and the water to replace at a percentage you choose.
Aquarium planning report
Enter measurements to generate the report.
Calculation method
Rectangle: inside length × inside width × actual water depth ÷ 1000 = litres. Cylinder: π × (inside diameter ÷ 2)² × actual water depth ÷ 1000 = litres.
Displacement defaults to zero; a user-supplied estimate reduces the geometric volume. The selected change percentage is applied to the estimated usable volume.
Source: Merck Veterinary Manual — Management of Aquarium Fish. Merck Veterinary Manual.
Important notes
- Use the actual water depth and inside dimensions: outside measurements can overestimate volume.
- Monitor water chemistry, temperature, ammonia and nitrite; volume alone cannot indicate tank health.
- The water-change percentage is your input, not a care recommendation.
Frequently asked questions
Does this calculate a safe number of fish?
No. Species, filtration, biological load, swimming space and water quality all matter.
What water-change percentage is best?
There is no universal number. Select a percentage based on your animals and measured water quality; the calculator only computes the volume.