Conversion to liquid volume in gallons

I have a cylindrical tank that lays in a cradle on it's side. The tank is 20 feet long and 5 foot 4 inches in diameter. I want to figure out the volume of the tank in gallons. I would also like to know how to extrapulate a table for gauging the tank from the top when it lays on its side and it would vary the per inch amount in the curve of the tank.

I have a cylindrical tank that lays in a cradle on it's side. The tank is 20 feet long and 5 foot 4 inches in diameter. I want to figure out the volume of the tank in gallons. I would also like to know how to extrapulate a table for gauging the tank from the top when it lays on its side and it would vary the per inch amount in the curve of the tank.

The formula for the volume of a cylinder is: PI*radius^2*length. It can also be written as: (PI*diameter^2*length)/4.

Assuming measurements are inside dimensions and the tank has flat ends:
Diameter: (5' * 12") + 4" = 64"
Length: 20' * 12" = 240"

(PI * 64"^2 * 240") /4,
(3.1415927 * 4096 * 240") /4 = 772,077.81 in^3
There are 231 in^3 in 1 gallon, so 772,077.81 in^3 / 231 in^3/gal = 3,342.33 gallons.

Calculating horizontal cylinder tank volumes by the inch is much more complicated. Go to http://vps.arachnoid.com/TankCalc/ and run the applet. Use inches for length units. If tank ends are flat, enter 0 in the "end cap radius" fields.

If you need further help, repost.

if you have a pipe that is 9.5 inches in diameter how long would the pipe need to be to equal 4 gallons.

if you have a pipe that is 9.5 inches in diameter how long would the pipe need to be to equal 4 gallons.

First, determine the gallons per inch, then divide gallons wanted by gallons per inch.

1) There are 231 cubic inches in a gallon (exactly) and 2) the formula for volume of a cylinder is: PI x radius squared x length.

Determine the gallons per inch:
PI x 4.75" radius squared x 1" deep = 3.1415927 * 22.5622 * 1 = 70.88219 cubic inches
70.88219 cubic inches / 231 cubic inches/gallon = 0.306849 gallons/inch

Determine length of pipe (in inches) needed to hold 4 gallons:
4 gallons / 0.306849 gallons/inch = 13.036 inches