For rectangular tanks: Measure the internal dimensions (length × width × height) for the most accurate results.

Tip: The actual water volume will be less than calculated due to:

• Substrate (gravel/sand): reduces volume by 5-10%
• Decorations and rocks: reduces volume by 5-15%
• Water level below rim: reduces volume by 5-10%

Pro tip: For the most accurate measurement, count how many litres/gallons you add when filling your tank for the first time!