2 to 180 Gallons Fish Tank Aquarium – How Many I Need?

How many Aquarium / Gallons (fish tank) do you need?

Looking for how big you need the fish tank to be? The Gallons Fish Tank is calculated based on how many fished will live within the habitat. If you are looking for an online calculator to convert Width, Height, Depth to Gallons of water needed for an aquarium, then we would recommend this page firsttankguide.net/calculator.php. Here you will find an online live calculator, for instance, that will give you an estimated amount of gallons needed to fill the fish tank of yours. Make sure to have in hand the measures in inches, for faster calculation.


Remember that the water needed in a fish tank should be about 10% to 15% less than the capacity of the aquarium. This is taken into account for many reasons including the dropping of the water out of the tank. Larger tanks are easier to clean, allow for extra food, extra decorations, and many other factors.

How much water or how many fish?

It is a normal question for fish owners and aquarium keepers to ask themselves about the capacity of their fish tanks. We wish each aquarium came with specifications and a table chart for the exact capacity for each one. But will you blindly trust it? Or will you research a little bit further?

As a result, we have found many overstock tanks, with a lot more fishes than it should have. We all know this story never ends pretty for the fishes inside. So we would like to talk about a few factors that need to be taken into consideration. Calculating the amount of stock to carry inside a fish tank and keeping the habitat safe.

Amount of Water Needed

The #1 and most popular method is called the One Inch Per Gallon of water. It’s widely used for a fast, inaccurate estimate for quick calculations. But this result should never be taken as a final decision. Time has changed a lot, nowadays we count on more efficient machinery. Equipment that make the habitat a much better place for the fishes and at the same time. It may vary the amount of fishes capacity. This is just to mention 1 factor that could alter the final amount of stock that an aquarium could carry. Other factors that affect the ecosystem, therefore, include the lighting, temperature, type of fish among many others.

As humans, the fishes are very different in needs, size, or even shape. We could spend the whole day explaining examples of how 5 big fishes could live perfectly in the same place where 10 small fishes could live perfectly too. So many of these factors of size, shape, and eating tendencies should be taken into account.

What about space to swim?

Humans like to swim, right? What about our fishes? That’s what they do best and they love to just swim around the whole time. This helps the fish to grow stronger, faster, and healthier. The fish tank should be big enough to allow the fish to swim freely back and forth among their partners.

One of the most beautiful things to see in a tank is a group of fishes swimming together in the same direction, and turning in the same direction all at the same time. Fish schooling is the correct term for this. It has a lot to do with the gallon per fish relation at the time of filling your tank. They need enough space to learn how to swim in a group and how to swim alone. This is often used as a method for self-protection as enemies will not feel as tempted when they find a big crowd of fishes swimming around.

Fish size and taking into account the growing

For a 1 inch fish maybe you will need less than a quarter amount of gallons of water than for the same fish after 1 year, maybe it grew up to 6 inches now and you need to adapt to the growth of your fished and their needs. Also, planning ahead of what sort of tank fish you will buy, for how many fishes you want, and how big they will get in time, so you don’t end up buying multiple fish tanks and having to separate family fishes that grew together into different tanks.

Take into account, that we as humans are not the only ones that get sad when get separated from family and friends. Many fishes create a strong bond among their family and neighbors who grew around them . With time, are considered as a family for them. If you plan to separate them into 2 small fish tanks, take into account to recognize which ones are able to be moved without affecting others. This is a life-changing decision for them. We would recommend just upgrading to a bigger fish tank, consequently, where all the fishes could get inside together and live happily ever after!

Water depth Importance in an Aquarium

The reason why we don’t like online “calculators” for fishes and gallons per fish needed in an aquarium is simple. These calculators, sometimes, don’t take everything into consideration. In this case, we want to talk about the water surface and depth.

Vertical Fish Tanks are very popular for decorations as they don’t occupy too much space, but at the same time, they don’t have much WATER SURFACE SPACE, this is where the oxygen exchange happens. Every fish needs to exchange oxygen with the exterior and this is when the rule of water surface comes into action. Remember that a tank that is tall and thin may hold the same amount of fishes as another one that is short but wide even tho they have different surfaces.

Now we will talk about the variety of gallon fish tanks that exist and what are they ussages.

2 to 180 gallons fish tanks

2 Gallons fish tanks:

(PRICE $10 to $20) In this small aquarium, you may have up to 2 small fishes living in there, with the right care and food, it should be enough. The 2 inches aquarium is most popular for 1 fish only. They might grow enough, after that, 2 fishes could be too much for a 2-gallon fish tank. Some customers rather buy the 2.5-gallon tank just as a precaution for the future growth of the fishes. Recommended fishes for this size tanks are Bloodfin Tetras, Cory Catfish, Betta Fish, Small Barbs, Small Tetras, White Cloud Mountain Minnow, Danios, Kuhli Loach.

5 gallons fish tanks:

(PRICE $15 to $35) Excellent size and at the same time, these are the most popular fish tanks for home-usage. Small, Compact, good looking and carry enough fishes to make your place feel alive. The most popular size is 14.2 x 11.5 x 10 inches and you may include fishes like Betta Fish (Betta splendens), Guppies (Poecilia reticulata), Cherry Shrimp (Neocaridina davidi), Mollies (Poecilia latipinna/Poecilia sphenops), Pygmy Corydoras (Corydoras pygmaeus), Neon Tetras (Paracheirodon innesi), Harlequin Rasbora (Rasbora heteromorpha)

10 gallons fish tanks:

(PRICE $21 to $50) If your apartment or house is spacy, you would rather go with the 10 gallons tank as it may carry more fishes and allow growth with no problem. With a capacity of carrying 10 small fishes, we still recommend starting with a few, maybe 1 or 2 if this is your first time having fishes under your responsability, then grow in quantity as you take practice. Recommended fishes for this size tank are Cory Catfish, Neon Tetra, Dwarf Gourami, Fancy Guppy, Betta Fish, Zebra Danio, Otocinclus catfish, Platy.

15 gallons fish tanks:

(PRICE $35 to $70) For a more ambitious project, the 15 gallons aquarium allows for a lot more fishes and starts to fill up the empty space you used to have on that wall in the living room. Adding a few water lights and decorations could improve the overall looks for the fishes and for the tank surroundings. Often seen in the standard 20″ x 10″ x 18″, but you can get it in many other shapes and sizes. For this size aquarium, you may buy the following fishes: Guppies (active live-bearing fish, males have vibrant colors), Tetras (schooling fish which come in a wide variety of colors), Danios (hardy and lively schooling fish), Barbs (lively, easy to care for schooling fish), Dwarf Corydoras (gentle bottom dwelling fish)

20 gallon long aquarium:

(PRICE $45 to $90) We consider 20-gallon aquarium a perfect size for someone incurring to aquarists hobbies or as a future job. It will allow you to have a good variety of fishes and an ecosystem to play with, along with, a very decent size for a single person to maintain. Recommended for this size tank, you may buy the following fishes: Platy, Swordtail, Molly Fish, Cory Catfish, Dwarf Gourami, Neon Tetra, Zebra Danio, Fancy Guppy.

30 gallons fish tank:

(PRICE $56 to $120) Mostly seen in its popular size of 36″ x 18″ x 12″ this aquarium is still considered home/medium tanks for fishes. This will allow for not only fishes but also plants! Recommended fishes for this size tank, you may buy the following fishes: Cichlids (Dwarf, South African, and South American), Tetras, Catfish species (Corys, Plecos, and Otos), Rainbowfish, Guppies, Gouramis, Rasboras, Mollies.

40 gallons fish tank:

(PRICE $65 to $135) The best characteristic for the 40 gallons aquarium is the fact that at this size, all secondary harmful effects from the chemistry changes in the water are minimized due to the huge amount of water in the tank. Help minimize the effects of temperature change by having much more water. For this sort of tanks, be ready to allow no more than 15 to 25 fishes. List of fishes Recommended for this size tank, you may buy the following fishes: Discus, German Blue Ram, Gourami, Diamond Neon Tetra, Endler’s Livebearer, Killifish, Boeseman’s Rainbowfish, Fantail Guppy.

50 gallons aquarium:

(PRICE $78 to $150) Tanks this big are often used more as decorative habitats, make sure you make space for it and be ready to decorate it accordingly. If a small tank would restrict your creativity fish plants, fishes, or decorative surroundings. This is right for you as it adds flexibility and freedom for new and grown fish species. Fishes good for a 50-gallon fish tanks: African Cichlids. African Cichlids, Angelfish. Angelfish, Goldfish. Goldfish, Gourami. Gourami Fish, Tetras. Neon Tetra, Barbs. Denison Barb, Rainbowfish. Rainbowfish, Ram Cichlids. Ram Cichlid.

60 gallons aquarium:

(PRICE $90 to $160) The most popular size measures 48.5” W x 12.75” D x 25” for 60 gallons aquarium. Cleaning is one of the topics that should be clarified for tanks this big. Remember to clean them at least once o twice a month. Don’t forget the water filter among other water cleaning details. These are the type of fishes you may introduce on a 60-gallon tank: Cardinal Tetra and other small tetra species. Dwarf Cichlids, such as Angel Ram cichlids (Microgeophagus ramirezi) or Apistogramma Borelli opal (Umbrella cichlidsRasbora such as Harlequin Rasboras. Dwarf Gourami species, like blue gourami or mosaic gourami.

75 gallons tanks:

(PRICE $100 to $700) Tanks this big could scare most home aquarists with the wrong conception. The real fact is that larger tanks are easier to maintain as it contains a lot more water. Makes your aquarium a lot more stable, after that, no matter the surrounding conditions. This makes this aquarium a perfect fit for beginners and also experienced aquarists. The number of fishes you could grow on a 75-gallon tank is about 25 to 35 fishes . You might see tank sizes ranging around 48.5″ x 18.5″ x 21.125″. Species that people tend to have on this 75-gallon size aquarium: Goldfish (Among their wide range of variety), Zebra Danios, and many other tropical fishes.

100 gallons tanks:

(PRICE $250 to $1,500) Size and dimensions will vary a lot for this amount of gallons fish tank as it starts to get unpractical for small spaces. We will see it around 50inch long by 20 wide by 20 high approx. At this size, people tend to order custom size aquarium instead of purchasing pre-made ones. Over 100 gallons of aquariums are seeing in restaurants and businesses rather than houses or apartments. Species that people tend to have on this size aquarium: Surgeonfish (like blue or yellow tangs), Dragonets, Frogfish, some of the smaller Butterflyfish, Clownfish, Damselfish, Hawkfish and Puffers.

125 gallons fish tanks:

(PRICE $300 to $1,750)

150 gallons Aquarium:

(PRICE $250 to $1,900)

180 gallons fish tanks:

(PRICE $500 to $2,000+) Over 180 gallons tank is considered a PRO aquarium. If you are not serious about taking care of fishes and water plants, consider downscaling. Most consider the weight of 180 gallons of water, cristal, fishes and other decorative objects around it. It may add up to 1 ton in eight, not good for apartments or 2nd floors. Usual measures for 180-gallon aquarium are 72″ x 24″ x 25″.