Buying advice
Aquarium Sizes, Dimensions & Weight Chart
Tank size tells you roughly how much water an aquarium holds. It doesn’t tell you how much space the tank takes up.
A 20 gallon high and a 20 gallon long both hold about 20 gallons, but they need different stands, different-length lights, and different lids. A 55 and a 75 are both about four feet long, yet the 75 sticks out several inches farther from the wall.
That’s why the actual dimensions matter.
The measurements below are listed as length × width × height. They’re common dimensions for framed glass aquariums, not guaranteed measurements for every tank sold under that size name. Check the exact tank before buying a stand, lid, canopy, or other equipment where fit matters.
Aquarium size and weight chart
| Tank size | Approx. dimensions, L × W × H | Approx. empty weight | Approx. filled weight | Typical stand footprint |
|---|---|---|---|---|
| 2.5 gallon | 12.2 × 6.1 × 8.1 in | 3 lb | 27 lb | Match exact tank |
| 5.5 gallon | 16.2 × 8.4 × 10.5 in | 7 lb | 62 lb | Match exact tank |
| 10 gallon | 20.3 × 10.5 × 12.6 in | 11 lb | 111 lb | About 20 × 10 in |
| 15 gallon | 24.3 × 12.5 × 12.8 in | 21 lb | 170 lb | About 24 × 12 in |
| 20 gallon high | 24.3 × 12.5 × 16.8 in | 25 lb | 225 lb | About 24 × 12 in |
| 20 gallon long | 30.3 × 12.5 × 12.8 in | 25 lb | 225 lb | About 30 × 12 in |
| 29 gallon | 30.3 × 12.5 × 18.8 in | 40 lb | 330 lb | About 30 × 12 in |
| 30 gallon | 36.3 × 12.6 × 16.8 in | 43 lb | 343 lb | About 36 × 13 in |
| 33 gallon long | 48.3 × 12.8 × 13.4 in | 46 lb | 382 lb | About 48 × 13 in |
| 38 gallon | 36.3 × 12.6 × 19.8 in | 47 lb | 427 lb | About 36 × 13 in |
| 40 gallon breeder | 36.2 × 18.3 × 17 in | 58 lb | 458 lb | About 36 × 18 in |
| 45 gallon | 36.3 × 12.6 × 23.8 in | 69 lb | 515 lb | About 36 × 13 in |
| 55 gallon | 48.3 × 12.8 × 21 in | 78 lb | 625 lb | About 48 × 13 in |
| 60 gallon breeder | 48.5 × 18.5 × 16 in | 43 lb | 543 lb | About 48 × 18 in |
| 65 gallon | 36.4 × 18.4 × 25 in | 90 lb | 775 lb | About 36 × 18 in |
| 75 gallon | 48.5 × 18.5 × 21.1 in | 98 lb | 785 lb | About 48 × 18 in |
| 90 gallon | 48.5 × 18.5 × 25.1 in | 135 lb | 1,050 lb | About 48 × 18 in |
| 125 gallon | 72.5 × 18.5 × 23.1 in | 177 lb | 1,400 lb | About 72 × 18 in |
| 150 gallon | 72.5 × 18.5 × 29.5 in | 281 lb | 1,800 lb | About 72 × 18 in |
Filled weight is an estimate, not the final weight of a finished aquarium. Substrate, rocks, wood, equipment, and water held in filters or sumps can add quite a bit.
Stand dimensions are approximate too. A matching footprint does not mean a stand can safely hold every aquarium with that footprint. Check both the dimensions and the stand’s rated capacity.
20 gallon long vs. 20 gallon high
The names make these tanks sound more alike than they are.
A 20 high is about 24 inches long and 17 inches tall. A 20 long is about 30 inches long and 13 inches tall. Both are around 12½ inches from front to back.
The 20 long spreads the same volume across more floor space. That gives you more horizontal swimming room, more room for rocks and wood, and a larger bottom area for plants or bottom-dwelling fish. It’s also easier to reach the substrate because the tank is shorter.
The 20 high takes up less wall space.
Their stands are different sizes. A stand made for the roughly 24 × 12 inch footprint of a 20 high is too short for a 20 long.
The 20 long instead shares its basic footprint with a 29 gallon. That becomes useful when shopping for stands, lids, and other equipment.
Both 20 gallon shapes come in at roughly 225 pounds when filled with water.
20 gallon long vs. 29 gallon
A 20 long and a standard 29 gallon are almost the same tank from the floor’s point of view.
Both are about 30 inches long and 12½ inches wide. The difference is height. The 20 long is around 13 inches tall, while the 29 is closer to 19 inches.
That extra height brings the 29 to roughly 330 pounds filled, about 100 pounds heavier than a 20 long.
A stand may physically fit both tanks because the footprints are so similar. It still needs to be rated for the heavier one.
These tanks also tend to use similar light lengths because both are about 30 inches long. Lids are less forgiving. Rim measurements can differ between brands, so measure before assuming one will fit.
Why the 40 breeder is different
A 40 breeder is about 36 inches long, 18 inches front to back, and 17 inches tall.
That 18-inch depth is the part that matters.
Many tanks in the 30 to 40 gallon range are only about 12 or 13 inches deep. The breeder gives you several extra inches from front glass to back glass without becoming especially tall.
It feels much larger inside than a narrow 36-inch tank. Rockwork can extend backward instead of being arranged in a thin line. Plants have more room. Fish have more usable horizontal space.
It also needs a deeper stand.
A narrow stand that happens to be 36 inches long is not enough. A 40 breeder needs support for its roughly 36 × 18 inch footprint and weighs around 460 pounds filled before substrate and décor are added.
This is one size where shopping by gallon count causes a lot of trouble. “40 gallon stand” does not tell you enough.
55 gallon vs. 75 gallon
Put a 55 and a 75 next to each other and the difference is obvious from the side.
Both are about 48 inches long. Both are around 21 inches tall.
A 55 is only about 13 inches deep from front to back. A 75 is about 18 inches deep.
Those extra inches change almost everything except the length.
A 55 uses a narrow four-foot stand. A 75 needs the wider 48 × 18 inch footprint. The 75 also gives you much more room for rockwork, wood, plants, and fish that need space to turn.
The weight jump is noticeable too. A filled 55 is around 625 pounds. A filled 75 is closer to 785 pounds.
They may use lights in the same general four-foot size range, but that doesn’t make their stands or lids interchangeable.
60 breeder, 75 and 90 gallon tanks
These tanks show why footprint and capacity have to be treated separately.
A common 60 breeder and a 75 both use roughly a 48 × 18 inch footprint. The 60 breeder gets its smaller volume by being shorter.
A standard 90 uses about the same footprint again, but stretches upward to around 25 inches tall.
From above, they can look like the same tank.
From underneath, the difference matters. A filled 60 breeder is a little over 500 pounds. A 75 is around 785 pounds. A 90 can reach roughly 1,050 pounds.
A stand can therefore have exactly the right dimensions and still be the wrong stand.
65 gallon vs. 40 breeder
A standard 65 gallon uses roughly the same 36 × 18 inch footprint as a 40 breeder.
Then it goes up.
The 40 breeder is only about 17 inches tall. A 65 is around 25 inches tall.
That makes the 65 appealing when floor space is limited but you still want more water volume. It also makes the tank much deeper to work in. Reaching the bottom of a 25-inch-tall aquarium is very different from reaching into a breeder.
Weight changes just as much. A 40 breeder is around 460 pounds filled. A 65 can approach 775 pounds.
Same floor space. Very different load.
125 gallon vs. 150 gallon
Common 125 and 150 gallon tanks can share roughly the same 72 × 18 inch footprint.
The 150 gets much of its extra volume from height.
A 125 is around 23 inches tall. A 150 can be close to 30 inches tall. The taller tank may look like a small change on a spec sheet, but it changes how the aquarium feels once it’s on a stand.
Reaching the bottom gets harder. Lighting the lower part of the tank becomes more demanding. The glass itself is heavier.
A filled 125 is around 1,400 pounds. A 150 can be near 1,800 pounds before a heavy aquascape is added.
At this size, “six-foot aquarium stand” is nowhere near enough information. The footprint has to match, and the stand has to be built for the actual load.
What size aquarium stand do you need?
Start with the aquarium’s footprint, not its gallon rating.
The footprint is simply the length and width of the tank where it meets the stand. A tank around 30 × 12 inches needs a stand built for that footprint. A 40 breeder needs roughly 36 × 18 inches. A 75 usually needs about 48 × 18 inches.
Then check the weight rating.
This is where tanks that share a footprint split apart. A 20 long and a 29 may fit the same size stand, but the 29 is heavier. A 75 and a 90 can occupy almost the same floor space, yet the 90 carries hundreds of pounds more water.
The top also needs to support the aquarium the way its manufacturer intends. Different tank designs can place their load differently.
Don’t choose a bookshelf, dresser, desk, or cabinet just because the tank fits on top. A filled 55 gallon aquarium is already around 625 pounds before gravel, rock, equipment, or extra water in a filter enters the picture.
How much does an aquarium weigh when full?
Fresh water weighs about 8.34 pounds per US gallon.
That gives you a useful starting point:
water weight = actual gallons of water × 8.34 lb
Then add the rest:
total setup weight = empty tank + water + substrate + rocks or wood + equipment + extra water
The last part is easy to forget. A canister filter, hang-on-back filter, or sump holds water outside the display tank. That water still weighs something.
The tank also rarely contains its full advertised volume of water. Glass thickness, substrate, rocks, wood, and the space left below the rim all reduce the amount you actually pour in.
This is why a simple “10 pounds per gallon” rule can be useful for rough mental math but shouldn’t decide whether a stand is suitable.
Tank dimensions also affect your equipment
Gallons get most of the attention when people shop for aquariums. Equipment often cares more about dimensions.
Lights are the obvious example. A 20 high is roughly 24 inches long, while a 20 long is roughly 30 inches. A 40 breeder is around 36 inches. Many 55, 75, and 90 gallon tanks are around 48 inches long.
Width matters too. A light that covers a narrow 55 well may behave differently over an 18-inch-deep 75, even though both tanks are four feet long.
Height changes how far light has to travel to the bottom and how easy the aquarium is to work in.
Lids and canopies are even more dependent on exact measurements. Two tanks sold under the same gallon size can have slightly different rims, braces, or outside dimensions.
Measure the exact tank when fit matters.
Tank prices and stock change too often to make sense as permanent article copy.
Show available aquariums grouped by size and footprint. Useful sizes to prioritize include 10 gallon, 20 long, 29 gallon, 40 breeder, 55 gallon, 60 breeder, 75 gallon, 90 gallon, and 125 gallon.
Group stands by footprint and rated tank size. Show the stand dimensions, stated weight capacity when available, and the aquarium sizes the manufacturer says it supports.
A deal module should match products using actual measurements and compatibility data, not gallon labels alone. A stand labeled for one 40 gallon tank may not fit a 40 breeder at all.