Gross vs actual volume
48 × 13 × 21 in multiplies out to 56.7 US gallons, but that box includes the glass and runs to the very top of the frame. Taking off 6 mm of glass on each side and the base, and filling to 1 inch below the rim, leaves about 50.9 gallons of water. Gravel, rock and wood take that down further; the volume calculator estimates it for your aquascape.
How much a filled 55 gallon weighs
| Water | ≈ 399 lb |
| Glass | ≈ 68 lb |
| Gravel (2 in) | ≈ 69 lb |
| Total | ≈ 536 lb |
|---|
Water weighs 8.34 lb per US gallon, so it is most of the load. Put the tank on a stand rated for it, level, and supported under the whole frame. More on this in how much a fish tank weighs.
Heater and filter
Holding 78 °F in a 68 °F room with a lid takes about 150 W of heater, using the same heat-loss model as the heater calculator (compare sizes on the heater size comparison). For filtration, a common target is turning the water over 4–6 times an hour: 204–306 gallons per hour of rated flow.
Frequently asked questions
What are the dimensions of a 55 gallon tank?
A standard 55 gallon aquarium is 48 × 13 × 21 in (length × width × height), or about 122 × 33 × 53 cm. These are outside dimensions; brands differ by a fraction of an inch.
How many gallons does a 55 gallon tank actually hold?
Its outside dimensions work out to 56.7 US gallons (215 liters). Inside the glass, with the water about an inch below the rim, it holds roughly 51 gallons (193 liters), and less once gravel and rock go in.
How much does a 55 gallon aquarium weigh when full?
Roughly 536 lb (243 kg): about 399 lb of water, 68 lb of glass and 69 lb for a 2 inch gravel bed. Rock, decor and the stand add to that.
What size heater does a 55 gallon need?
About 150 W to hold 78 °F in a 68 °F room with a lid. A colder room or an open top needs more; the heater calculator works it out for your conditions.