Standard Fish Tank Sizes Made Simple

Published February 11, 2020
Teenage girl cleaning sand in a home aquarium with a siphon pump

Shopping for an aquarium tank means determining not only the size of the tank, but the weight once it's filled with water, rocks, decorations and fish. It helps to go in knowing what standard size options, even if sizes may vary slightly between manufacturers.

Standard Aquarium Tank Sizes

When thinking about fish tank sizes, the first measurement you want to focus on is the number of gallons. While there can be some variation depending on who makes the tank, you will generally find tanks in the same gallon sizing.

  • Small aquarium tank sizes run from about 2-½ gallons through 15 gallons.
  • Medium aquarium tank sizes start at 20 gallons through 40 to 45 gallons.
  • Large aquarium tank sizes start around 50 gallons and can go up to 225 gallons.
New Empty Fish Tank

Aquarium Tank Dimensions

Not all tanks are made the same size so you'll find some variation in dimensions across manufacturers for tanks with the same gallon size. Usually these variations will be just by a few inches.

Fish Tank Size Chart

The following chart lists the sizes and commonly found tank dimensions. Some factors to consider when using this chart include:

  • The "empty" weight should be used as an approximate idea of the weight as this will fluctuate depending on the individual manufacturer's product specifications.
  • The full weight is also approximate as this will vary based on what you use to decorate the aquarium (i.e. live rock, decorations).
  • You also need to consider that there is a slight difference between the weight of saltwater and freshwater. A gallon of freshwater is about 8.34 pounds whereas a gallon of saltwater is about 8.54 pounds.
  • Mixing equipment from different manufacturers can also affect the final weight. If you like to add in a different type of light or a stronger filter system, expect your filled weight to change.
  • Weight may also vary depending on the thickness of the glass, so you could have two aquariums with the same dimensions but the one with thicker glass will be heavier at the empty and full weight.

Small Fish Tank Sizes

A small aquarium tank is good for smaller, freshwater fish. Smaller aquariums are easier to find spaces for in your home, but the smaller your tank ecosystem, the harder it is to maintain good water quality on a consistent basis. It's important to keep the number of fish in the tank appropriate to the size.

Small Fish Tank


Empty Weight (lbs)

Full Weight (lbs)

Dimensions (L x W x H)




  • 12" x 6" x 8"
  • 12-3/16" x 6-⅛" x 8-⅛"

5 - 5-1/2



  • 16" x 8" x 10"
  • 16-3/16" x 8-3/8" x 10-1/2"




  • 20" x 10" x 12"
  • 20-1/4" x 10-1/2" x 12-9/16"


21 - 22


  • 24" x 12" x 12"
  • 20" x 10" x 18"
  • 24-1/4" x 12 -1/2" x 12-3/4"
  • 20" x 10" x 18"
  • 20-1/4" x 10-1/2" x 18-3/4"

Medium Fish Tank Sizes

Medium fish tanks are good for freshwater fish, assuming the number of fish per gallons is appropriate to maintain a healthy tank. As you move into the medium size tanks, proper aquarium furniture is important as the weight of the tank increases substantially.

Fish Swimming In Aquarium At Home


Empty Weight (lbs)

Full Weight (lbs)

Dimensions (L x W x H)




  • 24" x 12" x 16"
  • 30" x 12" x 12"
  • 20" x 10" x 24"




  • 24" x 12" x 20"
  • 24-1/4 x 12-1/2 x 20-3/4




30″ ×12″ ×18″




  • 30" x 12" x 18"
  • 30-1/4 x 12-1/2 x 18-3/4




  • 36" x 18" x 12"
  • 36-1/4 x 12-5/8 x 16-3/4




36-1/4" x 12-5/8" x 19-3/4"


55 - 58

455 - 458

  • 36" x 18" x 16"
  • 48" x 12" x 16"
  • 36" x 13" x 20"
  • 48" x 13" x 16"
  • 48-1/4" x 12-3/4" x 16-7/8"

Large Fish Tank Sizes

As you get into the large tank sizes, you can start looking at saltwater fish and more elaborate ecosystem setups. You also will need to make sure the tank is well supported as large tanks can be very heavy and can put strain on furniture and the floor if you're not on the ground level.

Reef Tank Maintenance


Empty Weight (lbs)

Full Weight (lbs)

Dimensions (L x W x H)




  • 36" x 18" x 19"
  • 36-3/8" x 18-3/8" x 19"




  • 48" x 13" x 21"
  • 48-1/4" x 12-3/4" x 21"




48-3/8" x 12-7/8" x 23-7/8"




  • 36" x 18" x 24"
  • 36-3/8" x 18-3/8" x 25"
  • 36-7/8" x 19" x 24-5/8"




  • 48" x 18" x 21"
  • 48-1/2" x 18-1/2" x 21-1/8"




  • 48" x 18" x 24"
  • 48-1/2" x 18-1/2" x 25-3/8"




72-1/2" x 18-1/2" x 19-3/8"




72" x 18" x 21"




  • 72" x 18" x 28"
  • 72-1/2" x 18-1/2" x 28-1/2"




  • 72" x 24" x 25"
  • 72-1/2" x 24-1/2" x 25-5/8"




72" x 27-1/2" x 27-1/2"

Calculating the Gallon Size of a Tank

Sometimes you need to calculate how many gallons a tank can hold because it has unusual dimensions or you are receiving it second hand without accurate sizing information.

  1. The easiest way to do this is to use basic math to figure out the volume of the tank in cubic inches.
  2. A gallon of fresh water is 231 cubic inches so you just need to divide the volume by 231.
  3. To figure out the actual filled weight, multiply the gallon size by 8.34 for a freshwater tank and 8.54 for a saltwater tank.
  4. If you do not enjoy doing math, you can also use a handy online aquarium tank volume calculator to do the numbers for you.
  5. There are also online fish tank volume calculators that can convert from gallons to litres.

How to Measure For Your Tank

There are a few steps you should start with before you consider how many gallons your tank will be.

  1. The first thing you should do is take good measurements of the room where you want to keep your aquarium to make sure there's ample room for the tank and stand.
  2. Keep in mind too you want to have lots of room to move around the tank to do things like cleaning, set-up, and other care tasks that will be hard to do if your tank is scrunched into a tight space. You should measure for sufficient space behind and around the tank for you to do regular tasks.
  3. Make sure there is also enough room between the tank and the wall for any items that may stick outside of the dimensions, such as large filter, hoses and power strips.
  4. Determine the size of the tank stand or furniture that you will use to keep the stand on that will be in that space. If you already have the piece of furniture, it's important to find out from the manufacturer, if possible, what maximum weight it can hold. A tank filled with water is extremely heavy, especially as you go for larger and larger tanks. A piece of furniture that cannot meet that weight will easily sag and even collapse over time.
  5. Other things you'll want to consider when looking at the space is making sure it's not right up against direct sunlight, near any high activity events that might lead to disturbing or even breakage of the tank, and not accessible to pets. For example, you don't want your tank opening right next to your cat wall perch, though your cat will definitely appreciate it!
  6. Finally if the tank is a very large one, and it's on an upper floor, it's very important to make sure that the floor can support the weight. Some of the largest aquariums once filled with water, fish and decorations can weigh close to a ton or more. If you live in an apartment or condominium complex, there may be restrictions on how large of a tank you can have because of concerns about the weight's strain on the floor.
Family cleaning reef tank

Finding the Right Tank Size for Your Aquarium

Make sure you take your time doing proper measurements before you buy your tank and ensure that the water weight can be supported by your furniture and your floor! While it may seem like extra work, you will be glad you took the time to measure. Having a huge, heavy tank that's too close to a wall for easy cleaning and maintenance can become a pain to deal with very quickly. Once a tank is filled with water, decorations and fish, moving it is not a simple matter. Use the chart and the calculators to ensure you have the best aquarium size and weight for your home situation so you can enjoy a stress-free aquarium experience.

Trending on LoveToKnow
Standard Fish Tank Sizes Made Simple