by Dirtman » Wed Jun 20, 2007 10:09 am
The formula for calculating the volume of a cylinder in gallons (with perpendicular ends) using inches is: PI*R^2*L/231
where:
PI = 3.1415927
R = radius in inches
L = length in inches
231 = cubic inches in a US gallon
so:
3.1415927 * 8 * 8 * 37.5 / 231 = 32.64 gallons
However, most pressure tanks have semi-elliptical tank ends plus an expandable bladder, which allows the tank to hold pressure when a pump isn't on. The above formula does not account for the semi-elliptical tank ends or a pressure bladder.