Math CentralQuandaries & Queries


Subject: I need math help pleaseeee.
Name: Taye
Who are you: Parent

I am building a aquarium for my daughter, It is 6 feet long 24 inches high and only 5 inches wide. How many gallons will it hold?

Also my main goal is to build a aquarium that will hold 40 gallons but have similar dimensions as the ones I stated above. What should I change to achieve this?

Thank you for taking the time to help me because I am totally lost on this.

We have two responses for you.


I know the number of cubic inches in a gallon so I would first convert the length to 6 x 12 = 72 inches. Hence your aquarium has a volume of

72 x 24 x 5 = 8640 cubic inches.

I can't complete the solution to your problem because I don't know where you live. It seems strange that the answer to a question in mathematics depends on where you live but an american gallon contains 231 cubic inches and a british gallon contains 277.4 cubic inches. Divide by 231 or 277.4, whichever is appropriate, to obtain the number of gallons your aquarium will hold.

In both cases you obtain a volume of something less than 40 gallons and you need to make a decision. Increase one, two or all three of the dimensions a little and redo the calculations until you get dimensions that please you, and a volume of 40 gallons.


Hi Taye.

If you are using the american "gallon", there are 231 cubic inches per gallon. If you are using the larger UK "gallon", there are 277.4 cubic inches per gallon.

Since 6 ft is 6x12 = 72 inches, the dimensions you describe gives 72 x 24 x 5 = 8640 cubic inches. Using american gallons, that is 8640 / 231 = 37.4 gallons.

A 40 gallon tank can be achieved many ways. If you want to retain the 5" and 24" dimensions, then 40 x 231 / 5 / 24 = 77 inches. That means extending the tank to 6' 5"

Hope this helps,
Stephen La Rocque.

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