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Page 2 about

How to Calculate Aquarium Volume

This page contains Customer Comments and our Replies about How to Calculate Aquarium Volume.

Click here to go back to the first page in this discussion about Calculating Aquarium Volume.


Customer Comments

I really love your website, honestly. I've taken virtually all your advices into account and managed to successfully sustain my tank. Great, keep on the good pace.
But Hold on, there's a major setback in this website, the English System MUST GET RID OF THIS VILE NOW PLEASE! Where I live we use logic, an aqaurium that is 60cm in legth, 40cm height, 20cm wide boasts a volume of 48 liters, hence 40 x 60 x 20= 48,000 cubic cm, divided by a thousands and walla you get 48 liters!
I've also attented an american school and I know that AMericans are not that stupid and if they really want they could grasp this type of unit too. Trust me on this!
Naomi G.
Reply. Hello Naomi and thank you for your advice. I'm sure you are right, but I just can't seem to think metric.

I like the fact my foot is about a foot long, and a digit in my finger is about an inch long, and there are many other things in the foot, inches, and pounds way of doing things that seem more intuitive to me, even if the math is less convenient.

The aquarium in your example is about 16" x 24" x 8" = 4/3 ft. x 2 ft. x 2/3 ft. = 16/9 cubic feet. Multiply by 25/3 to convert cubic feet to gallons: 16/9 x 25/3 = 400/27. Which I can "see" is about 15-gallons. Actually I did all of this in my head, and did it quite fast.

On the other hand I can get the 48 liters fast just like you did. Next I know a litter is about 5/4 of a quart or 5/16 of a gallon, and 48 x 5/16 is again easy to "see" is 15-gallons.

But I'm more used to doing it in inches.

Thank you for trying to help me.


Customer Comments

Just received and read my first issue of your e-mail newsletter (#4) What a great info filled missive! Thank you for awakening me to this source. I will be on your list forever ( and will become a buyer also) I am sure.
In the section "how to measure a fish tank", Naomi G has chosen to request a change to metric measurements. She states that she uses logic ( I assume that means our 50 states don't) and she has "attented" an American school and we (Americans) are not stupid and should start thinking in metric.
She is correct: I should understand metric. I am not stupid. However, I, like her, make calculations in my head using the system I was brought up using. I need reference books and a calculator to understand the metric system.
Please do not go metric unless you provide both standards. 
Reply. Hello Graham. Thank you for your email and for your comments about the metric system. We're glad that you enjoyed our newsletter.

Customer Comments

I was just searching to find out how to calculate the volume for my aquarium. The trouble I'm having is that my tank is a hexagon, and the measurements of it do not appear to be standard.
Do you know how I would measure the width?
The longest width is 25.5" and the 6 panels are 12" long. The depth I believe is 24" (from flat edge across to flat edge). The height is 24.75".
Could you please help me?
Thank you,
Reply. Hello Karen. Lets calculate the volume of your aquarium, which has a hexagon for the base and a height of 24.75".

Click here to see a picture of a hex-aquarium.

The formula for volume is always the base times the height, which you measured 24.75". So all we need is the area of the base.

Since all 6 panels in your aquarium are 12", the base is a so-called regular hexagon with all the sides measuring 12".

The area of this regular hexagon is 6 times the area of an equilateral triangle with each side 12".

Now think of a 12" equilateral triangle, and divide into two right triangles  with one side 6" and hypotenuse 12".

The other side will have a length equal to the square root of 12x12 - 6x6, which equals the square root of 144 - 36, which is the square root of 108, or about 10.4".

The area of the right triangle is 1/2 x 6 x 10.4, and the area of the equilateral triangle will be twice as much, which is 6 x 10.4 = 62.4 square inches, so the area of the base of your aquarium is 6 x 62.4, or 374.4 square inches.

The volume of your aquarium is the area of the base times the height = 374.4 x 24.75 = 9296.4 cubic inches.  Now multiply by 0.00433 to convert cubic inches to gallons:

9296.4 x 0.00433 = 40.1 gallons, which answers your question.

When you calculate something like this, and the answer is important, because you may use the answer to determine how much Quick Cure or Salt to add to your aquarium, then it's best to double check your calculation.

Or you might end up forgetting that the equilateral triangle has two right triangles, and get an answer that is off by a factor of 2.

Here is one way to double check the answer. The hexagonal base of your aquarium could fit inside a circle with a radius of 12" and have an area of about

pi x 12 x 12 = 3.14 x 12  x 12 = 452.2 square inches

which is somewhat bigger than the 374.4 square inches for the area of the hexagon inside the circle. So that checks.

A circle with a radium 10.4" would fit inside the hexagon, and that circle would enclose an area of about

pi x 10.4 x 10.4 = 3.14 x 10.4 x 10.4 = 327.8 square inches

which is less than the 374.4 square inches for the area of the hexagon. So that checks too.

Also the area of the hexagon should be about half-way between the area of the inner circle and the area of the outer circle.

The areas are about 327.8, 374.4, and 452.2, so those numbers look about right.

Now lets check these calculations with a measurement. Your aquarium is 24.75" tall.

When you change 20% of water, as recommended repeatedly in this website, you should remove 20% x 24.75 = 4.95, or about 5" of water.

So measure down from the water surface 5" and put a mark on the glass with a marker pen.

Now remove water down to the mark and keep track of how much water you remove. For example, you could use a clean one-pint measuring cup.

You should get close to 64 pints, which is the same as 8 gallons, or 20% of the 40-gallons, that we calculated in your aquarium. (Be sure to thoroughly clean the measuring cup, when you finish using it.)

You will probably measure less than 64 pints. Maybe you'll get 61.

Because the measurements for your aquarium that you gave in your email were probably the outside measurements, and the water fills the inside of your aquarium.

You could improve the calculations above by doing them again with the inside measurements, and perhaps subtracting the volume of the ornaments, etc. Click here for more about doing that.

I hope this has thoroughly answered your question.


Customer Comments

Thank you!!!!
I would like to thank you so much for responding. My calculations came out similar, when I focused on the formulas, but I was still unsure if I was doing it correctly.
I couldn't find a 40 gal hex listed anywhere I looked on the Internet, so I kept doubting my answer.
I also tried marking the water line and removing a gallon of water, and then measuring. I was really close to 40 gal. again.
I haven't had to add any medications to my tank as yet, (knock wood) but that possibility, and calculating the amount of fish I can put in there safely, is why I needed confirmation.
Thanks again,
Reply. Hello again Karen. Thank you for your reply. I'm glad to know that you made your own calculations and measurements, and agree with you, that knowing the volume of your aquarium in gallons is important.
Click here to go to another web page in this site with more comments about Measuring and Calculating about Aquariums.
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