Math CentralQuandaries & Queries


Question from Jerry:

I want to build A tank. able to hold 400 gallons of asphalt sealer it will be round . basically like A old fuel oil drum but made with heavy material . math ? was I want tank to hold 400 gallons I think the length of 60" would be perfect. I don’t know what diameter or radius of tank needs to be . to make it A 400 Gallon tank


There are two common uses of the term gallon. One US gallon is 231 cubic inches and one Imperial gallon is 277.42 cubic inches. I am going to assume that you mean a US gallon. If not then replace 231 in my calculations by 277.42 and redo the arithmetic.

The volume of a cylinder is π r2 h where r is the radius, h is the height and π is approximately 3.1416. You have a volume of 400 × 231 cubic inches and a height (length) of 60 inches so the formula gives

π × r2 × 60= 400 × 231 cubic inches.

dividing both side by π × 60 I get

r2 = (400 × 231)/(π × 60) = 92400/188.50 = 490.20 square inches.


r = √490.20 = 22.1 inches.

Now that you have the radius you can check that the volume is about 400 gallons using our volume calculator.


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