How Many Gallons Of Water In Cylinder 4 Inches In Diameter And One Foot Long?

First let us make all the units constant. I am going to convert all the units into inches.
Therefore, the dimensions of the cylinder are:

Diameter = 4 inches
Length = 1 foot = 12 inches

Let's find its volume now:

Volume = base area x height

Base Area = pi x r²
  = 3.14 x (4/2)²
  = 3.14 x 2²
  = 3.14 x 4
  = 12.56 inch²
Volume = 12.56 x 12
  = 150.72 inch³

This is the volume in cubic inches. To find the volume in gallons, divide this answer by 231.
Volume in gallons = 150.72/231
  = 0.65 gallons

Therefore, there are 0.65 gallons of water in the cylinder.