Last update: December 12, 2023

Aquarium Volume Calculator: How Many Gallons Can Your Tank Hold?

Want to know how much water your aquarium can hold?

Use our handy calculator to find out just how many gallons (or liters) of water your aquarium is capable of holding.

Notes on Aquarium Capacity:

Now that you know the volume of water that your aquarium can hold, you will want to be mindful of one fact:

Your aquarium will never actually hold this much water.

For instance, I have never met anyone who fills their aquarium all the way to the top of the tank. Any gap that you leave here will mean that there is less water in your tank.

Also, anything that you place in your tank will remove the same amount of water. Fish, rocks, coral, substrate, decorations… These all mean that there is less water in your tank.

Think of it as though you are filling your bath to the top with water and sliding in – the water is going to overflow because your body is taking up space where the water previously was.


Fish Tank Sizes: What Are the Common Fish Tank Sizes?

Fish tank sizes vary from small 2.5-gallon desktop tanks to over 300-gallon tanks for larger setups. I would say the right size for you depends on available space and the fish species you would like to keep.

How Many Gallons Is My Tank?

To find out the number of gallons your tank can hold, you’ll need to measure its length, width, and height in inches and use an aquarium volume calculator.

How Many Gallons Is an 8x8x8 Tank?

An 8x8x8 tank measures 8 inches in length, 8 inches in width, and 8 inches in height. If you would like to calculate its volume in gallons, simply multiply these dimensions and divide by 231 (cubic inches per gallon). In this case, an 8x8x8 tank can basically hold  2.62 gallons.

Aquarium Volume Calculator: How to Use It?

Using an aquarium volume calculator is pretty straightforward. Enter your tank’s dimensions in inches, and the calculator will provide you with the total gallon capacity.

Aquarium Size: Does It Impact the Number of Fish You Can Keep?

Yes, your aquarium size is an important factor. A larger tank can support more fish and offer you better water quality and stability. Smaller tanks are usually suitable for a limited number of small fish or specific species.

4 Feet Tank How Many Gallons?

A 4 feet tank usually comes in different dimensions. Measure the length, width, and height in inches, and then you can use the aquarium volume calculator to determine the precise gallon capacity.

3ft Tank How Many Gallons?

Similarly, for a 3ft tank, you should measure its dimensions and employ the aquarium volume calculator to ascertain the number of gallons it can accommodate.

In a Nutshell

Knowing the gallon capacity of your tank is important and will help you in creating a healthy aquatic environment regardless of your status as beginner or an experienced fish keeper.

Fish tank sizes can vary widely, and accurately determining the gallon capacity is a fundamental step. When you employ an aquarium volume calculator, it simplifies the task and allows you to efficiently find the gallon capacity of your tank and any tank, whether it’s a 4 feet tank, a 3ft tank, or even an 8x8x8 tank.

You should always remember that your fish tank size directly impacts the number and type of fish you can maintain, so make sure you choose wisely to ensure the well-being of your aquatic companions.

I hope this was helpful. Even if you’re only buying betta, it’s a good idea to calculate how much water you’ll need for its fish tank.

Ian Sterling

Ian Sterling, founder of, began his aquarium journey over 30 years ago, driven by a deep fascination for fish and their diverse personalities. His website,, is dedicated to making fishkeeping accessible and enjoyable, offering beginner-friendly guidance, expert insights, and a community for aquarists to connect and share experiences.

Comments (37)

Great calculator. Exactly what I was looking for. I was buying a new tank this weekend and now I know the water amount in the tank.

Hi Jane,

All you have to do is measure your aquarium and the calculator above will do the rest. A single dimension isn’t enough for me to give you an answer as to how much water your tank can hold.

Hi Miachael,

For chemicals such as water conditioner, yes the sump is included. Let’s say you had a 100 gallon display tank and a 30 gallon sump. You would use 130 gallons when figuring out your dosage. Obviously this does not take into consideration any water displaced by decorations, rocks, driftwood, corals etc, so the reality is that the actual amount of water in your tank is less. As always, make sure you follow the instructions carefully when adding any chemical into your tank.

Easy to calculate got 5 feet length and 2 feet depth and 2 feet width fish tank. Before loading with accessories wanted to know the gallons or litres of tank. Above calculator was a great help To identify

Hello sir,

My brother and I are setting up a 5 feet in length, 2 feet depth and 2 feet width aquarium which we will only place 1 silver aroana. My brother said he will only use a filter and he was wondering how strong the filter is. The Watts?

I find it hard to believe that a 20x20x20 tank in cm is the same size as a 20x20x20 tank in inches. Please explain

Hi Bill,

You are correct. It looks like something has gone wrong with the calculator. I’ll have my developer fix it up ASAP. For now the inches to gallons is working correctly.

I purchased a tank used he told me it was 120 g when I looked at it seemed larger I measured it The measurment was 24 “×24″ ×60” so aprox
150 g and how much did it weigh had to bring it out to the truck then down to twisting steps
Either 270 lbs or 330 I have to figure out how to move it onto the bar top my self My brother inlaws will not move it again I suppose I will Mcguiver it 1

I would like to use a tank that is set in angle iron frame, the tank measures 183cmX61cmX61cm, I can obtain 6mm glass. And do I need to put Kaolite (a sheet of expanded soft material) at the base, as it has a 2mm iron sheet at the base, welded in place.
Your advice would be most appreciated.

Hi Rob,

Unfortunately, I don’t give construction advice via my blog. I highly recommend joining an online forum, where you can discuss the pros and cons of such a design.

Any suggestions on what kind of fish food that will not cloud the water…
I had 12”x21”x60” aquarium…
My fish is butterfly koi and goldfish…

Hi Oscar,

It’s unlikely that the fish food is the problem. It’s your stocking. You have too many fish for your aquarium. Read up on ALL the basics, like cycling your aquarium, how many fish can fit etc.

Thank you for help , I bought a tank from a friend that is 36”wide by 24” high by 12”deep. Your quick calculating system is great!! Thanks again for your help.

Hi Jiec,

It depends on the temperature outside the tank vs. The temperature you want your tank raised to. The difference here in conjunction with the size of your tank is what determines the size of the heater needed in watts.

Im trying to set up a 32 gallon water tank for 2 hatchling size turtles i dont know where to start or what to buy

Hi Barbie,

Your best bet would be to head to your local fish store (not a big box chain like petsmart or petco) and ask them, exactly what you need will vary according to where you are setting up and a whole host of other factors – you’ll get the best advice there.

Thank u so very much for ur site. I have been buying tanks from my yard sale on line because they are more affordable for me but i also like different shaped or size tanks. i bought two tanks that i really liked but didnt no the gallons until now. i have a 58 gal tank. 25x18x30 thank you again for this site

Hi Jenifor,

I’m glad I could help. For cheap tanks, I highly recommend keeping an eye out for Petcos dollar per gallon sale, they happen regularly and you can pick up some good aquariums at a budget price.

Thank you for confirming gallon size of my bow front. I bought off Craig’s list and now have to look for a stand. It seems 40 g bow front stands are hard to come by without paying a fortune, if indeed I can find one. Thanks again for your help

Thank you. I have been thinking of updating my tank but I have to take into consideration the size of the tank. I have had my present 36 gal tank for over 20 years.

Hi Eli,

Good question. Once you get to this size, have determined it’s in your price range and don’t want to build one yourself, your best bet is to reach out to a local aquarium manufacturer.

Going local (if possible) will save on freight as it can be expensive to ship tanks of this size across the country. However, depending on where you are located, this may not be possible. In this case, reach out to a site like glasscages

Also, at this price range, it may not be more expensive to customize the shape of the tank – this way you can be sure that it fits your living arrangements perfectly.

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