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 Question from gordon, a parent: What is the formula to find out how many gallon of water in a length of pipe tried your answer on 8inch at 50feet did not work out

Hi Gordon,

The formula for the volume of a circular cylinder is $\pi \; r^2 h$ where $\pi$ is approximately 3.1416, $r$ is the radius of the cylinder and $h$ is its height. I am going to use inches as the units since I know that one US gallon is 231 cubic inches.

I assume that the 8 inch pipe has an 8 inches inside diameter and hence its inside radius is 4 inches. There are 12 inches in a foot an hence the volume of the pipe is

$\pi \; \times 4^2 \times 50 \times 12 = 30159.289 \mbox{ cubic inches}$

which is

$\frac{30159.289}{231} = 130.56 \mbox{ gallons.}$

If you would rather not do the calculation yourself you can use our volume calculator.

Penny

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