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55 Gallon Tank Dimensions
A standard 55 gallon aquarium measures about 48 × 13 × 21 in (122 × 33 × 53 cm) on the outside. Exact sizes vary by brand: Aqueon lists 48¼ × 12¾ × 21 in and Marineland 4815⁄32 × 1227⁄32 × 2013⁄16 in. Once it's set up with 2 inches of sand, it holds roughly 44 gallons of water and weighs about 500–510 lb in total.
55 gallon tank calculator
Drawn to scale from your numbers: sand at the bottom, water up to your fill line.
Setting up a 55?
- Plan your fish: the stocking calculator checks numbers and tank mates
- Size your heater for your room temperature
- Check another tank's volume, any shape
Not every 55 gallon is the same size
The “55 gallon” label is a class of tank, not an exact measurement. Here is what each source actually lists:
| Source | L × W × H (in) | Empty | Full |
|---|---|---|---|
| Aqueon size chart | 48¼ × 12¾ × 21 | 78 lb | 625 lb |
| Marineland ML10556 (dealer listing) | 4815⁄32 × 1227⁄32 × 2013⁄16 | 62 lb | 521 lb |
| SaltwaterAquarium.com size table | 48 × 13 × 21 | 78 lb | – |
Checked 24 Sep 2026. Marineland's full weight is simply the label gallons × 8.34 lb plus the empty tank; Aqueon's is closer to the full outside volume filled with water. Neither includes sand, rock or the stand. That's why the two brands disagree.
Same stand, two tanks
The 55 shares its narrow 48 × 13 footprint with the 40 long. The 75 is the same length but 5¾ in deeper, so it does not fit a 55 stand.
| Tank | L × W × H (in) | Outside volume |
|---|---|---|
| 40 gallon long | 48 × 13 × 16 | 43.2 gal |
| 55 gallon | 48¼ × 12¾ × 21 | 55.9 gal |
| 75 gallon (different stand) | 48½ × 18½ × 21⅛ | 82.1 gal |
Aqueon size chart (55, 75); Marineland dealer listing (40 long, nominal).
55 vs 75: why so many people upgrade
Both are 4 ft long and about 21 in tall. The difference is depth: 12¾ in against 18½ in. That extra 5¾ in front to back gives:
- About 21 more gallons of actual water (our estimate, with 2 in of sand).
- Room to turn for larger-bodied fish, and space for aquascapes with depth instead of a single row of plants.
- A different stand. A 55 stand can't take a 75, so an upgrade usually means a new stand too.
The 55's strength is its footprint: it fits along a wall where an 18 in deep tank would stick out.
How much water a 55 gallon really holds
Multiply the outside dimensions of an Aqueon 55 and you get 55.9 gallons. You never get that much water, because of three things:
- Glass. With about 5/16 in glass (an estimate; check your tank), the inside is roughly 47⅝ × 12⅛ in.
- The gap at the top. Most people keep the water about an inch below the rim.
- Substrate. Two inches of sand takes up about 19 litres of space.
That leaves about 49.2 gallons with a bare bottom and 44.2 gallons with 2 in of sand. Use the real figure, not the label, when you dose medication or water conditioner.
Weight and stand
A set-up Aqueon 55 comes to about 514 lb: 78 lb of glass, about 369 lb of water and about 67 lb of sand, before rock and the stand itself. That sits on 4.3 square feet.
- A set-up 55 weighs about 514 lb. Use a stand made for 48 × 13 tanks and rated above that.
- Where you can, place it across the floor joists and near a load-bearing wall. On older or upper floors, ask a builder first.
General guidance, not structural advice.
Equipment for a 55 gallon
| Item | Starting point | How we got it |
|---|---|---|
| Heater | 133–221 W | 3–5 W per gallon of real water; use the higher end in a cold room. |
| Filter | 177–265 gph | Turning over the water 4–6 times an hour |
| Sand, 2 in deep | ≈ 67 lb | Inside floor area × depth at about 1.6 kg per litre (estimate) |
| Light | 48 in | Match the tank length |
| Lid | 2 × 24 in (48 × 13) | Check the maker's fit list |
Rules of thumb, not guarantees. Fish choice, room temperature and filter type all change the right answer.
What a 55 gallon is good for
Four feet of length suits active schooling fish, but the 13 in depth limits larger-bodied fish. Check any mix in the stocking calculator.
How the numbers are worked out
Worked examples
Aqueon 55, 5/16 in glass, 1 in gap, 2 in sand: inside 47.62 × 12.12 in, water height 21 − 0.3125 − 1 − 2 = 17.69 in. 47.62 × 12.12 × 17.69 = 10,214 in³ ÷ 231 = 44.2 gal (167.4 L).
Marineland 55, 5/16 in glass, 1 in gap, 2 in sand: inside 47.84 × 12.22 in, water height 20.8125 − 0.3125 − 1 − 2 = 17.5 in. 47.84 × 12.22 × 17.5 = 10,230 in³ ÷ 231 = 44.3 gal (167.6 L).
Bare-bottom Aqueon 55, 5/16 in glass, 1 in gap, 0 in sand: inside 47.62 × 12.12 in, water height 21 − 0.3125 − 1 − 0 = 19.69 in. 47.62 × 12.12 × 19.69 = 11,369 in³ ÷ 231 = 49.2 gal (186.3 L).
FAQ
What are the dimensions of a 55 gallon tank in feet?
About 4 ft long, just over 1 ft deep and 1¾ ft tall (48 × 13 × 21 in).
How much does a 55 gallon tank weigh full?
Aqueon lists 625 lb and Marineland 521 lb. Our estimate with 2 in of sand is about 514 lb before rock.
Will a 55 gallon stand hold a 75 gallon tank?
No. Both are 48 in long, but the 75 is about 18½ in deep against the 55's 12¾ in.
How many litres is a 55 gallon tank?
55 US gallons is 208 litres. Set up, expect about 167–187 litres of actual water.
Do a 40 long and a 55 use the same stand?
Yes, both sit on a 48 × 13 in footprint. Check the stand's weight rating for the 55.
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Sources
- Aqueon aquarium size and weight chart, aqueon.com (PDF): www.aqueon.com
- Marineland standard aquariums, Bluefish Aquarium (dealer): bluefishaquarium.com
- Marineland 55 Gallon ML10556, Bluefish Aquarium: bluefishaquarium.com
- Aquarium Weights & Sizes, SaltwaterAquarium.com: www.saltwateraquarium.com
- All accessed 24 Sep 2026. Calculations by TankRatio; “estimate” and “rule of thumb” figures are ours.