Math CentralQuandaries & Queries


Subject: water
Name: bryan
Who are you: Other

How many gallons of water does an 8 inch pipe that is 50 foot long hold?

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

length = 50 x 12 = 600 inches and
radius = 4 inches.

The volume V of a cylinder is

V = π r2 h

where r is the radius and h is the height (length). Thus the volume of water in your pipe is

V = π 42 x 600 = 30,159.29 cubic inches.

Hence the volume in US gallons is 30,159.29/231 = 130.56 gallons.


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