How Much Does A 20 Gallon Fish Tank Weigh?

How Much Does a 20 Gallon Fish Tank Weigh? Fish tanks can be extremely heavy when they are full of water. So before filling a used or new tank, it would be best to know how heavy the aquarium will be so you can ascertain the cabinet, table, or stand—and even the floor itself—is up to the aquarium’s load.

These types of fish tanks are highly recommended for beginner fish keepers. Anything in the range of 20 to 40 gallons has a sufficient volume that will minimize hazardous effects due to changes in chemistry in your aquarium water. In order to manage a nice stock of fish it will be too big.

Again, these aquariums are not so huge that cleaning will be a big issue. It is necessary because a lot of people who are new to the fishkeeping world find that keeping up with fish with maintenance will become overwhelming. Overall, the mid-sized aquariums are a manageable, nice size.

Following are a few rough guidelines as to what to expect while looking at a fish tank and its full vs. empty weight. The weights are just a rough estimate because the amount of rock, type of water, and thickness of glass all affect the calculations of weight.

A freshwater gallon at a particular gravity of 1.000 weighs 8.34 lbs. 1 gallon of water 8.34 lbs times the specific gravity of say 1.025 equals 8.5485lbs (8.43 x 1.025 = 8.5485).

The weight of the water will directly go proportionate to the weight of the salt that is being dissolved in the water. 1-gallon saltwater at 1.025 equals 8.54 lbs.

How heavy is a 20 gallon fish tank?

Tank SizeL x W x HEmpty WeightFilled Weight
20-gallon (high)24″ x 12″ x 16″25 lbs.225 lbs.
20-gallon (long)30″ x 12″ x 12″25 lbs.225 lbs.

Calculating the Weight of Custom-Shaped Tanks

Apart from basic rectangles, aquariums may be in the shape of pentagons, hexagons, or even cylinders. If you are going to own such an aquarium, the volume in gallons will already be specified. You can use the charts above to calculate the full and empty weight of the aquarium.

A 50-gallon aquarium will have the exact weight measurements whether it is hexagonal, rectangular, or cylindrical in shape.

But if you have been given or buying a used aquarium and do not know the size of the gallon, calculating the weight of the tank and gallon volume is actually just a matter of first calculating the cubic inches of volume. The key measure one should know:

  • 1 gallon of water = 231 cubic inches

If you can measure the volume of any fish tank in cubic inches, then it would be very easy to translate that into a gallon capacity. Once you have calculated the gallon capacity, use the above-mentioned charts to estimate the full and empty weight of the aquarium.

It requires a little math to determine the volume. The volume of a fish tank is measured by first figuring out the area of base shape in square inches, and then multiplying it by the height.

The simplest way to do this is to sketch out the shape of the base of your tank and, after that divide it into shapes which have areas that can easily be determined.

For example, a hexagon can be divided into triangles and rectangles. You have to figure out the area of each shape in inches and after that add them together to figure the area of the aquarium’s base shape. To calculate the actual volume in cubic inches, multiply this number by the height of the tank.

The next step is to divide the total cubic-inch volume by 231 to figure out the gallon capacity of your tank.

Finally, find a corresponding capacity of gallon in the charts listed above to calculate the approximate weight of your fish tank.

How much does a 20 gallon fish tank weigh? Well, basically this depends on what the tank is made of (acrylic, glass, etc.).

Believe it or not, it also depends on the temperature of the tank water… a gallon (US gallon) of water weighs 8.34lbs when its temperature is at 17 C or 62F

But, assuming that the tank is holding a FULL 20 gallons of water and it is at that temperature it would roughly weigh-

20*8.34=166.8lbs or 167lbs

If you add on a few more pounds for the aquarium itself, I would say that it’s approximately 170–175lbs (If all the above-mentioned conditions are fulfilled)

The weight of fresh water is 8.3 pounds each gallon. So the 20-gallon tank weighs more than 166 pounds plus the weight of the gravel, glass, and frame and it will be dangerous to move. Place your tank where you want it to be placed and fill it afterward. When compared, salt water weighs more than fresh water at 8.6 pounds each gallon.

Is a 20 gallon fish tank big?

A 20 gallon aquarium or fish tank is super perfect for new aquarists. These tanks are sufficiently large to have a decent selection of fish, yet too small to maintain.

A 20 gallon tank allows you to keep a wide range of different fish, as well as some other inhabitants such as shrimps or snails and live plants.

How Much Does a 20 Gallon Fish Tank Weigh (Summary)

Freshwater177 lbs167 lbs
Saltwater181 lbs171 lbs
20 Gallon Fish Tank Weight Calculation Table

A 20 gallon glass tank that measures 24” x 13” x 16” will approximately weigh 177 pounds while it is filled with fresh water.

When the same glass tank, is filled with saltwater, then it will weigh 181 pounds.

An acrylic fish tank with the exact measurements will weigh 167 pounds when it is filled with fresh water, and 171 pounds when it is filled with saltwater.


Dibyajyoti Bordoloi is the creator and author of, a third-generation experienced fish keeper and owner of a successful pet breeding farm. He is also a member of the Center for Wildlife Rehabilitation And Conservation (Assam), the Marine Aquarium Societies of North East India, and the Kaziranga Nature Conservancy of Assam.

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