How Many Gallons Is Your Fish Tank?
Calculate aquarium volume in gallons and liters from tank dimensions. Rectangular, bowfront, and cylindrical tanks.
Why Exact Volume Matters
Knowing your exact aquarium volume is critical for: medication dosing (fish medications are dosed per gallon — overdosing kills fish), water conditioner (treats X gallons per cap), stocking levels (fish per gallon rules), and heater sizing (watts per gallon). The stated tank size from the manufacturer is nominal — actual water volume after substrate and decorations is 10-15% less.
Weight Considerations
Water weighs 8.34 lbs per gallon. A 55-gallon tank weighs approximately 625 lbs when filled (water + glass + substrate + decorations). This exceeds the typical floor load rating of upper floors in many homes. Tanks over 30 gallons should be placed on the ground floor or on a reinforced stand, ideally perpendicular to floor joists.
Subtract 10-15% from your calculated volume for the "real" water volume after substrate, rocks, wood, and equipment displace water. A 20-gallon tank with 2 inches of gravel and a few decorations holds about 17-18 gallons of actual water.
