I have to keep an inventory of how much is kept in a farm of tanks outside my school. The tanks are cylindrical, which would be no problem if they were standing on end, but they're not, they're lying on their sides. xx x x x----------x -Liquid level which is variable, x x can go up or down x x x x x x xx Imagine the above is a circle. I know the diameter of the circle, and I can measure from the top of the circle down to the liquid level. How can I use this information to derive the amount of liquid in the circle? I hope to make a formula I can use in a spreadsheet. Thanks so much.