Gross vs actual volume
24 × 12 × 16 in multiplies out to 19.9 US gallons, but that box includes the glass and runs to the very top of the frame. Taking off 5 mm of glass on each side and the base, and filling to 1 inch below the rim, leaves about 17.6 gallons of water. Gravel, rock and wood take that down further; the volume calculator estimates it for your aquascape.
How much a filled 20 gallon high weighs
| Water | ≈ 135 lb |
| Glass | ≈ 26 lb |
| Gravel (2 in) | ≈ 32 lb |
| Total | ≈ 192 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 75 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: 70–105 gallons per hour of rated flow.
Frequently asked questions
What are the dimensions of a 20 gallon high tank?
A standard 20 gallon high aquarium is 24 × 12 × 16 in (length × width × height), or about 61 × 30 × 41 cm. These are outside dimensions; brands differ by a fraction of an inch.
How many gallons does a 20 gallon high tank actually hold?
Its outside dimensions work out to 19.9 US gallons (76 liters). Inside the glass, with the water about an inch below the rim, it holds roughly 18 gallons (66 liters), and less once gravel and rock go in.
How much does a 20 gallon high aquarium weigh when full?
Roughly 192 lb (87 kg): about 135 lb of water, 26 lb of glass and 32 lb for a 2 inch gravel bed. Rock, decor and the stand add to that.
What size heater does a 20 gallon high need?
About 75 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.