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Aquarium Volume Calculator & Fish Tank Dimensions (How Many Gallons)

Aquarium Volume Calculator & Fish Tank Dimensions (How Many Gallons)

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Aquarium Volume Calculator (How Many Gallons)

There are various reasons you might want or need to use an aquarium volume calculator:

  • Determine the true volume of a custom aquarium 
  • Find the true volume of an off-the-shelf fish tank
  • Decide the necessary dimensions of a custom tank install
  • Help in selecting an appropriate equipment such as:
    • Return Pumps
    • Sump Size
    • Reactor Flow
    • Skimmer Size
    • etc.

Rectangular Aquarium Volume Calculator

Cylindrical Aquarium Volume Calculator

How do I figure out how many gallons of water?

Mathematical Formulas to calculate Cubic Inches and Convert to Gallons of Water

Cubic Volume = Length x Width x Height

Length x Width x Height in inches will give you the number of cubic inches in a given rectangular volume.

Cylindrical Volume = π r2 h

Pi x Radius Squared x Height in inches will give you the number of cubic inches in a given cylindrical volume.

1 cubic inch of water = 0.004329 gallons of water

To convert cubic inches to gallons of water simply multiply by the total cubic inches by 0.004329.

Uniquely shaped aquariums will require a bit of thinking to calculate the number of gallons they hold. A bow front, for instance, can be calculated by measuring the rectangular section first. Next measure the bow front section as if it were rectangular and divide it by two. 

Suggested Reef Tank Sump Size

To calculate how many gallons of water your sump will hold it’s important to understand that the sump should be able to hold a certain amount of water while the pump is flowing and also be able to hold all of the water in the plumbing and above the drain in your display tank. When your return pump isn’t running all of the water in the plumbing will flow down to the sump so if you don’t account for how much water is in your piping, you could end up with water flooding onto your floor.

Be sure to check out our article that explains everything you need to start a saltwater aquarium.

Popular DC Return Pumps

How Much Does A Gallon Of Saltwater Weigh

How Much Does A Gallon Of Freshwater Weigh

Tank Care Essentials

Common Fish Tank Dimensions (Standard Aquarium Sizes)

While we can’t obviously cover every possible aquarium, this is a fair comprehensive list of typical tank sizes. These dimensions should be able to be a very helpful guide for designing your next setup or making changes to your existing one.

2.5 gal
(12″ x 6″ x 8″)


5.5 gal
(16″ x 8″ x 10″) 


10 gal
(20″ x 10″ x 12″) 


15 gal
(24″ x 12″ x 12″)


16 gal high
(20″ x 10″ x 18″) 

20 gal high
(24″ x 12″ x 16″) 


20 gal long
(30″ x 12″ x 12″)


29 gal
(30″ x 12″ x 18″) 


30 gal
(36″ x 13″ x 16″) 


37 gal
(30″ x 12″ x 22″) 


40 gal breeder
(36″ x 18″ x 16″) 


40 gal high
(36″ x 12″ x 21″)


53 gal
(36″ x 18″ x 21″) 


55 gal
(48″ x 13″ x 20″) 


60 gal
(48″ x 13″ x 24″) 


65 gal
(36″ x 18″ x 24″) 


75 gal
(48″ x 18″ x 21″) 


90 gal
(48″ x 18″ x 24″) 


110 gal
(48″ x 18″ x 30″) 


120 gal
(48″ x 24″ x 24″) 


120 gal X-high
(60″ x 18″ x 26″) 


125 gal
(72″ x 18″ x 22″) 


150 gal
(72″ x 18″ x 27″) 


150 gal X-high
(48″ x 24″ x 31″) 


180 gal wide
(72″ x 24″ x 24″) 


220 gal wide
(72″ x 24″ x 30″) 


265 gal
(84″ x 24″ x 30″)

2.5 Gallon

12″ x 6″ x 8″

5.5 Gallon

16″ x 8″ x 10″

10 Gallon

20″ x 10″ x 12″

15 Gallon

24″ x 12″ x 12″

16 Gallon High

20″ x 10″ x 18″

20 Gallon High

24″ x 12″ x 16″

20 Gallon Long

30″ x 12″ x 12″

29 Gallon

30″ x 12″ x 18″

40 Gallon Breeder

36″ x 18″ x 16″

40 Gallon High

36″ x 12″ x 21″

53 Gallon

36″ x 18″ x 21″

55 Gallon

48″ x 13″ x 20″

60 Gallon

48″ x 13″ x 24″

65 Gallon

36″ x 18″ x 24″

75 Gallon

48″ x 18″ x 21″

90 Gallon

48″ x 18″ x 24″

110 Gallon

48″ x 18″ x 30″

120 Gallon

48″ x 24″ x 24″

120 Gallon Extra High

48″ x 18″ x 30″

125 Gallon

72″ x 18″ x 22″

150 Gallon

72″ x 18″ x 27″

150 Gallon Extra High

48″ x 24″ x 31″

180 Gallon Extra Wide

72″ x 24″ x 24″

220 Gallon Extra Wide

72″ x 24″ x 30″

265 Gallon

84″ x 24″ x 30″

What Size Aquarium Is Best?

The bigger the aquarium the more stable the water parameters will be, which in turn makes for a more stable environment for your fish and corals. You might say that the best size aquarium is the biggest one your budget and space can accommodate.

You’ll need to consider the additional equipment you’ll need for a larger aquarium. For instance, my previous 40-gallon Red Sea aquarium required a single light. The 120-gallon I replaced it with required adding another 2 lights. I have a 180-gallon aquarium on the way to replace the 120 and I won’t need to purchase any more lights, fortunately.

Lights aren’t the only thing that increases with aquarium size. Pumps, skimmers, heaters, powerheads, sumps, etc. all have to be increased in size and/or number to properly address the larger physical dimensions and increased water volume.

Another consideration is the frequency and amount of effort required when maintaining tanks of different sizes. Small tanks tend to require a much lower effort but more frequently. Large tanks require a higher effort but less often.

For instance, a 20% water change in a 40-gallon aquarium is only 8 gallons. Performing a 20% water change on my incoming 180-gallon aquarium will require draining and replacing 36 gallons of saltwater.

You’ll want to keep all of this in mind when you’re making a decision for what size aquarium is best for you and your situation. I advocate for 75 gallons or more if you can and I wouldn’t go any less than 40 gallons unless you’re an expert. Below 40 gallons and you really need to stay on top of things almost daily.

Can A Fish Tank Be Too Big?

When aquariums begin to get really large, what you need to consider, in addition to the cost of the tank itself and equipment as well as the maintenance effort, is the weight of the tank, stand, equipment, and water.

You need to ensure that your floor can support the massive amount of weight. If the floor underneath your aquarium will be a concrete slab you have nothing to worry about. But if you’re going to be placing your aquarium on a second floor or on the first floor with a crawl space you should begin to consider contacting a structural engineer when an aquarium is larger than 125 gallons.

Is A Tall Or Wide Fish Tank Better?

In general, a wider tank is better than a taller aquarium. There are some species of fish or invertebrates that may prefer more water depth but almost all fish are going to prefer having more length for swimming.

When tanks get taller than the length of your arm they become much more difficult to clean. They can require tools to reach the bottom and I can tell you from experience, these tools are a lot less user-friendly than just reaching in and doing what you need to do.

Another consideration with tall tanks is you may need more powerful lights to provide proper lighting to corals placed lower in the aquarium since the light will have to penetrate through a deeper amount of water.

In Conclusion

These aquarium volume calculators and fish tank dimensions hopefully will prove helpful in selecting appropriately sized equipment. Knowing a more accurate volume for your aquarium will provide more accurate results with your reef.

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