Will my fish tank fall through the floor?

Fish tanks can be surprisingly heavy when they are full of water. Before filling a new or used tank, it is best to know how heavy it will be so you can ensure the cabinet, table—and even the floor itself—can handle the load.

Here’s the thing:

It is unlikely that your fish tank will fall through the floor, but you can’t rule out the possibility. Heavier aquariums can cause severe structural damage as the pressure causes the water to fall out and ruin the floor. 

You can make sure your fish tank doesn’t fall through the floor by calculating the aquarium load capacity. Read on to find out more about the recommended floor load limit and aquarium sizes.   

Can Floors Support Big Fish Tanks?

Floor support depends on several factors, including the floor layout and aquarium size. You don’t need to worry about floor safety unless you have a monster-sized fish tank holding 150 gallons. You can easily place fish tanks with less than 60 gallons of water anywhere in your home. If you have a strong structural foundation and no framing defects, you can also place up to a 125-gallon tank with no problems! Avoid placing anything larger than 150-gallons on your floor without reinforcing it with extra bracing. Here are some guidelines on aquarium sizes:


Basic Aquarium Sizes

Aquariums come in different sizes and range from 2.5 gallons to 300 gallons. That is a massive range, so finding the right size depends on your goals and floor layout.

The chart below details the most common aquarium sizes, including empty and filled weight information. This is an important consideration for people interested in larger tanks. Keep in mind that 1 gallon of water equals 8.34 pounds, so you need to ensure that your floor can handle the weight of your new aquarium. A 175-gallon aquarium, when filled with water, accessories, and gravel, weighs over 2,000 pounds.

The weights mentioned are for glass aquariums; acrylic aquariums will weigh less. Also, exact dimensions may vary by brand and the trim used on the fish tank. It is best to take a measuring tape with you to the store to get exact measurements of your choice of an aquarium and double-check that your floor or cabinets can support it.  


Small Sized Aquariums

Small Aquariums
Tank SizeL x W x HEmpty WeightFilled Weight
2.5-gallon12″ x 6″ x 8″3 lbs.27 lbs.
5-gallon16″ x 8″ x 10″7 lbs.62 lbs.
10-gallon (leader)20″ x 10″ x 12″11 lbs.111 lbs.
15-gallon24″ x 12″ x 12″21 lbs.170 lbs.
15-gallon (high)20″ x 10″ x 18″22 lbs.170 lbs.
Small Aquariums

Experts recommend 5-gallon tanks as the minimum tank size for just one fish. Tanks under 5 gallons (like fishbowls) are susceptible to fluctuations in pH and buildups of waste materials and harmful chemicals. They also lack the critical surface area for healthy gas exchange and are stressfully small for even one fish. Fish can become distressed and vulnerable to disease when they don’t have enough room to swim. However, small fish tanks aren’t utterly useless! They are vibrant homes for beautiful aquatic algae and plant life, including trendy marimo moss balls (fluffy balls of algae that can live for decades). Tanks that hold up to 10 gallons have their challenges; due to their small capacity, diligent pH monitoring and good filtration will be necessary. You shouldn’t face any floor issues with small aquariums.


Mid-Sized Aquariums

Medium-Sized Aquariums
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.
25-gallon24″ x 12″ x 20″32 lbs.282 lbs.
29-gallon30″ 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.
Medium-Sized Aquariums

Professionals recommend mid-sized aquariums for beginners. Anything in the 20 to 40 gallon range is ideal for residential floors and has a sufficient volume to minimize harmful effects for fish. Mid-sized fish tanks are large enough to handle a nice school of fish.    

Also, these tanks are simpler to maintain and clean. This is important because many beginners find it hard to keep up with the maintenance. Overall, the mid-sized tanks are a great, manageable size.


Large Aquariums

Large Aquariums
Tank SizeL x W x HEmpty WeightFilled Weight
50-gallon36″ x 18″ x 19″100 lbs.600 lbs.
55-gallon48″ x 13″ x 21″78 lbs.625 lbs.
65-gallon36″ x 18″ x 24″126 lbs.772 lbs.
75 gallon48″ x 18″ x 21″140 lbs.850 lbs.
90-gallon48″ x 18″ x 24″160 lbs.1050 lbs.
125-gallon72″ x 18″ x 21″206 lbs.1400 lbs.
150-gallon72″ x 18″ x 28″308 lbs.1800 lbs.
180-gallon72″ x 24″ x 25″338 lbs.2100 lbs.
Large Aquariums

The larger your aquarium, the more fish you can keep. That is a nice advantage, but it also means that you will have to work twice as hard to maintain these tanks. You also have to think of the tank size when it comes to weight when filled. You need to make sure your cabinet and floor can handle such heavy loads. Owners of massive tanks may even find that floor reinforcement is critical to support a load that is in such excess.

If you want a diverse aquarium, bigger tanks have a better appeal. However, you also need to consider the tank’s scale in relation to your room and its surroundings. Is there enough room for hoses, joists, and accessories between the tank and wall? Can the floor handle the filled weight of the tank? These are important questions to ask before investing your time and money.


Calculating Weight of Custom-Shaped Aquariums

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

The key measure to remember:

1 gallon of water = 231 cubic inches

If you can measure any fish tank volume in cubic inches, you can translate it into a gallon capacity. Once you’ve determined the gallon capacity, you can use the charts to calculate the tank’s empty and full weight.

Determining tank volume requires a little math. You can estimate the volume by figuring out the base area in square inches, then multiplying this figure by the height. For example, you can divide a hexagon into rectangles and triangles and calculate each shape’s area and then add them together to figure out the total area of the tank’s base shape. Multiply this figure by the height of the tank to calculate the total tank volume in cubic inches. Next, divide the total volume by 231 to find the gallon capacity of your tank. Lastly, find a corresponding gallon capacity in the charts shared above to find the approximate weight for your fish tank.

Final Thoughts

Most residential floors can support a 125-gallon fish tank with ease, provided it sits on a sturdy wooden or metal stand. You can strengthen your floors by adding bracing between the joists. Experts recommend placing your fish tank against a load-bearing wall to eliminate the need for floor reinforcement.

Frequently Asked Questions

Why does my aquarium water level drop?

The temperature difference between the air and the water speeds up the water evaporation. As a result, the water level in the aquarium drops steadily.

Can a residential floor collapse from a heavy tank?

Office buildings can handle more weight than a residential home floor. If you don’t install load-bearing supports on your residential floor, it may collapse.

How to get clean and clear aquarium water?

Chemical filtration is the most common way to keep aquarium water clean.

Why are my floors sagging?

Poor structural support is the most common reason behind sagging floors. When your floor joists start to bend due to the overlying material’s pressure and weight, your floor will start sagging. The best way to fix the sagging floor is by installing new support structures.

How much weight can the second-floor hold?

The weight capacity of a second floor is about 40 lbs. per square foot. For bedrooms, the weight capacity is 30 lbs. per square foot.

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