Aquarium heater calculator

These bands (3 W/gal up to 10°F, 4 between 10 and 15°F, 5 at 15–20°F) are estimates, not manufacturer guarantees. Covers, drafts and evaporation matter. For rises above 20°F, use the maker’s sizing chart. Split heating above 55 gallons; verify temperature with a separate thermometer. Unplug heaters before exposing them during maintenance.

Worked example: 20 gallon long

20 nominal gal × 3 W/gal = 60 W for a mild rise; × 5 = 100 W for a larger rise. At a 10°F rise the rounded choice is 1 × 75 W.

Fluval heater guidance

Choose a tank size

• 2.5 gallon12 × 6 × 8 in
• 5 gallon16 × 8 × 10 in
• 5.5 gallon16 × 8 × 10 in
• 10 gallon20 × 10 × 12 in
• 13 gallon widescreen24 × 8 × 19 in
• 15 gallon24 × 12 × 12 in
• 15 gallon column13.75 × 13.62 × 25 in
• 20 gallon high24 × 12 × 16 in
• 20 gallon long30 × 12 × 12 in
• 20 gallon extra high20 × 10 × 24 in
• 25 gallon24 × 12 × 20 in
• 29 gallon30 × 12 × 18 in
• 30 gallon36 × 12 × 16 in
• 33 gallon long48 × 13 × 13 in
• 37 gallon30 × 12 × 22 in
• 38 gallon36 × 12 × 20 in
• 40 gallon breeder36 × 18 × 16 in
• 40 gallon long48 × 12 × 16 in
• 45 gallon36 × 12 × 24 in
• 50 gallon36 × 18 × 19 in
• 55 gallon48 × 13 × 21 in
• 60 gallon breeder48 × 18 × 16 in
• 65 gallon36 × 18 × 24 in
• 75 gallon48 × 18 × 21 in
• 90 gallon48 × 18 × 24 in
• 110 gallon48 × 18 × 30 in
• 120 gallon48 × 24 × 24 in
• 125 gallon72 × 18 × 21 in