How Size Affects an Aquarium's Weight

Illustration depicting the weights and tank sizes of aquariums
Illustration: Catherine Song. © The Spruce, 2018 

Fish aquariums can be surprisingly heavy when they are full of water, so before filling a new or used aquarium, it's best to know how heavy it will be so you can ensure the table, cabinet—or even the floor itself—is up to the load. 

Basic Aquarium Sizes

Aquariums come in many sizes, from as small as 2.5 gallons to as large as 180 gallons or more. That's a wide range, so finding the right one for you is going to depend on your goals and your level of experience.

The charts below detail the most common aquarium sizes, including size and empty weight information in U.S. units, as well as the weight when the tank is filled with water. This is an important consideration, especially for larger tanks. Keep in mind that one gallon of water weighs 8.34 pounds, so you need to ensure that your cabinet and floor can handle the weight of your aquarium.

This information will also help you guide several decisions, such as determining how much space is required, how much substrate and the amount of lighting you will need, recommended filter sizes, and other equipment needs. Also, keep in mind that the surface area of the water in the tank will determine how many fish you can stock.

The weights given are for glass aquariums; acrylic aquariums will weigh somewhat less. Also, exact dimensions can vary by brand and the trim used on the aquarium. It's best to take a tape measure with you to the fish store to get exact measurements and to ensure that all your accessories—particularly tank hoods and cabinets—fit properly.

Small Aquariums

Contrary to what you might think, small aquariums are not recommended for beginners. These small environments are very temperamental, so a tiny change in the chemistry of the water—ammonia, pH, etc.—can have a big impact.

If you do decide to keep a small fish tank, keep in mind that it will have a much smaller bio-load, so it's important that you do not overstock it with too many fish.

Also, because it is such a sensitive environment, good filtration is absolutely essential on small tanks.

       Tank Size    L x W x H    Empty Weight      Filled Weight   
   2.5-gallon12" x 6" x 8"3 lbs27 lbs
   5-gallon16" x 8" x 10"7 lbs62 lbs
  10-gallon Leader     20" x 10" x 12"  11 lbs111 lbs
  15-gallon   24" x 12" x 12"  21 lbs170 lbs
 15-gallon High   20" x 10" x 18"  22 lbs170 lbs

Mid-Sized Aquariums

These are the aquariums that are most often recommended for beginners. Anything in the 20- to 40- gallon range has a sufficient volume that will minimize harmful effects due to chemistry changes in the water, and will be large enough to handle a nice stock of fish.  

Also, these tanks are not so large that cleaning will be difficult. This is important because many people who are new to aquariums find that keeping up with maintenance soon becomes overwhelming. Overall, the mid-sized tanks are a nice, manageable size.

   Tank Size     L x W x H   Empty Weight     Filled Weight   
  20-gallon High   24" x 12" x 16"  25 lbs225 lbs
  20-gallon Long   30" x 12" x 12"  25 lbs225 lbs
  25-gallon   24" x 12" x 20"  32 lbs282 lbs
  29-gallon   30" x 12" x 18"  40 lbs330 lbs
  30-gallon Breeder     36" x 18" x 12"   48 lbs348 lbs
  40-gallon Breeder     36" x 18" x 16"   58 lbs458 lbs
  40-gallon Long   48" x 12" x 16"   55 lbs455 lbs

Large Aquariums

The larger the aquarium, the more fish you can stock. That's a decided advantage, but it also means that you'll have to work harder to maintain these tanks. Tanks of this size also come with concerns over weight when they're filled, so make sure your floor and cabinet can handle such heavy loads. Owners of very large tanks may even find that floor reinforcement is necessary to support a load that is in excess of one ton.

Bigger tanks have a great appeal, especially when you want to create a diverse aquarium. However, you also need to consider the tank's scale in relation to the room and its surroundings. Is there enough room for hoses and accessories between the tank and wall? Is it a high-traffic room? Are there space constraints that might lead to accidents and broken glass?

Do you have shelves overhanging the tank that may fall down and create an emergency for your fish? These are important questions to ask before making such a significant investment with your time and money.

Tank Size  L x W x H  Empty Weight     Filled Weight   
  50-gallon  36" x 18" x 19"  100 lbs600 lbs
  55-gallon  48" x 13" x 21"  78 lbs625 lbs
  65-gallon  36" x 18" x 24"  126 lbs772 lbs
  75 gallon  48" x 18" x 21"  140 lbs850 lbs
  90-gallon  48" x 18" x 24"  160 lbs1050 lbs
  125-gallon    72" x 18" x 21"  206 lbs1400 lbs
  150-gallon    72" x 18" x 28"  308 lbs1800 lbs
  180-gallon     72" x 24" x 25"  338 lbs2100 lbs

Calculating Weight of Other Shapes

In addition to basic rectangles, fish tanks may be in the shape of hexagons, pentagons, or even cylinders. If you are buying such a tank, the volume in gallons will already be specified and you can use the charts above to calculate the empty and full weight of the tank. A 50-gallon fish tank will have the same weight measurements whether it is rectangular, hexagonal, or cylindrical in shape.

But if you are buying or have been given a used tank and don't know the gallon size, calculating the gallon volume and weight of the tank is really just a matter of first calculating the cubic inches of volume. The key thing to know:

  • 1 gallon of water = 231 cubic inches 

If you can determine the volume of any tank in cubic inches, it's easy enough to translate this into a gallon capacity. You can then use the charts above to estimate the empty and full weight of the tank.

The volume of a tank is determined by first figuring out the area of the base shape in square inches, then multiplying this by the height. The easiest way to do this is by sketching out the shape of the base, then dividing it into shapes whose areas can easily be calculated. A hexagon, for example, can be divided into rectangles and triangles—calculate the area of each shape and add them together to figure the area of the tank's base shape. Then multiply this figure by the height of the tank to calculate the total volume in cubic inches.


Next, divide the total cubic-inch volume by 231 to find the gallon capacity of the tank. Finally, find a corresponding gallon capacity number in the charts above, and read across to find the weight figures for your tank.