How Size Affects an Aquarium's Weight

A 180-gallon fish tank weighs over 1 ton

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 is best to know how heavy it will be so you can ensure the table, cabinet—and 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 is 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. A 180-gallon aquarium, when filled with water, gravel and accessories, weighs over 2,000 pounds.

This information will also help you guide several decisions, such as determining how much space is required, how much substrate and 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. To be more precise, it is best to take a tape measure with you to the fish store to get exact measurements of your choice of tank and double-check 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 can be very temperamental, so a tiny change in the chemistry of the water, like ammonia or pH changes, 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 biofiltration capacity, so it is important that you do not overstock it with too many fish. Also, because it is such a sensitive environment, good filtration is absolutely essential for small tanks.

Small Aquariums
Tank Size L x W x H Empty Weight Filled Weight
2.5-gallon 12" x 6" x 8" 3 lbs. 27 lbs.
5-gallon 16" x 8" x 10" 7 lbs. 62 lbs.
10-gallon (leader) 20" x 10" x 12" 11 lbs. 111 lbs.
15-gallon 24" x 12" x 12" 21 lbs. 170 lbs.
15-gallon (high) 20" x 10" x 18" 22 lbs. 170 lbs.
Sizes and weights of aquariums up to 15 gallons

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.

Medium Aquariums
Tank Size L x W x H Empty Weight Filled 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.
25-gallon 24" x 12" x 20" 32 lbs. 282 lbs.
29-gallon 30" x 12" x 18" 40 lbs. 330 lbs.
30-gallon (breeder) 36" x 18" x 12" 48 lbs. 348 lbs.
40-gallon (breeder) 36" x 18" x 16" 58 lbs. 458 lbs.
40-gallon (long) 48" x 12" x 16" 55 lbs. 455 lbs.
20 to 40 gallon capacity

Large Aquariums

The larger the aquarium, the more fish you can stock. That is a decided advantage, but it also means that you will have to work harder to maintain these tanks. You also have to be concerned with tanks of this size when it comes to weight when filled. You need to 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.

Large Aquariums
Tank Size L x W x H Empty Weight Filled Weight
50-gallon 36" x 18" x 19" 100 lbs. 600 lbs.
55-gallon 48" x 13" x 21" 78 lbs. 625 lbs.
65-gallon 36" x 18" x 24" 126 lbs. 772 lbs.
75 gallon 48" x 18" x 21" 140 lbs. 850 lbs.
90-gallon 48" x 18" x 24" 160 lbs. 1050 lbs.
125-gallon 72" x 18" x 21" 206 lbs. 1400 lbs.
150-gallon 72" x 18" x 28" 308 lbs. 1800 lbs.
180-gallon 72" x 24" x 25" 338 lbs. 2100 lbs.
50 gallons and larger sizes

Calculating Weight of Custom-Shaped Tanks

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 do not 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 measure to know:

  • 1 gallon of water = 231 cubic inches 

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

To determine volume requires a little math. 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 to sketch out the shape of the base, then divide it into shapes that have areas that can easily be calculated. For example, a hexagon can be divided into rectangles and triangles. Calculate the area of each shape in inches and then add them together to figure the area of the tank's base shape. Multiply this number 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 in the charts above to find the approximate weight for your tank.