



 
Hi Bryan, One US gallon is 231 cubic inches. (If you are looking for British imperial gallons there are 277.42 cubic inches in a gallon.) An 8 inch pipe has a diameter 8 inches and hence a radius of 4 inches, hence you have a cylinder that has
The volume V of a cylinder is
where r is the radius and h is the height (length). Thus the volume of water in your pipe is
Hence the volume in US gallons is 30,159.29/231 = 130.56 gallons. Penny  


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