Aquarium Volume Calculator
Calculate aquarium water volume in gallons or liters from tank dimensions.
Supports rectangular, cylindrical, and bow-front shapes.
Aquarium volume is calculated from your tank’s dimensions using basic geometry, then converted to gallons or liters so you can properly stock fish and dose treatments.
Rectangular tank:
Volume = Length × Width × Height
Cylindrical tank:
Volume = π × (Diameter / 2)² × Height
What each variable means:
- Length — the longest side of a rectangular tank, or the diameter for cylindrical tanks, measured in inches or centimeters.
- Width — the front-to-back measurement of a rectangular tank (not used for cylindrical).
- Height — the water depth of the tank from bottom to top.
Unit conversions:
- Imperial: 1 cubic inch = 0.004329 US gallons (231 cubic inches per gallon)
- Metric: 1 cubic centimeter = 0.001 liters (1,000 cm³ per liter)
When to use this calculator: Use it when setting up a new tank, choosing the right filter or heater, calculating medication doses, or figuring out how many fish your tank can support.
Practical example: A rectangular tank measures 36 × 18 × 24 inches. Volume = 36 × 18 × 24 = 15,552 cubic inches. In gallons: 15,552 × 0.004329 = 67.3 gallons. After subtracting 12.5% for substrate and decorations, usable volume is about 58.9 gallons.
Stocking guidelines:
- Freshwater: roughly 1 inch of fish per gallon (2.5 cm per 4 liters)
- Saltwater: roughly 1 inch of fish per 5 gallons (2.5 cm per 20 liters)
Tips: Always use the usable volume (not total volume) when calculating fish capacity, medication dosing, or fertilizer amounts. Decorations, substrate, rocks, and equipment typically reduce actual water volume by 10–15%. Taller tanks have the same volume as shorter, wider tanks but provide less swimming area per gallon.