Horizontal cylindrical tank with both ends curved to form a ball is widely used for pressurized systems. Theoretically spherical tank is two times stronger than cylindrical tank. But the spherical tank is extremely difficult to build and expensive. Therefore, cylindrical tank is built with both ends or heads are curved or hemispherical, to increase the strength of the tank with the cost of fabrication is not very expensive.
The attached Excel spreadsheet has formula to calculate the volume of liquid for each fluid depth in a horizontal cylindrical tank with hemispherical shape at both ends or heads. The chart shows that the percentage of the volume does not form a linear line. It needs to be considered if you need to specify the minimal and maximal value of stock.
The formula used is similar to the formula in a horizontal cylindrical tank with both ends flat. There are only additions to calculate the volume on the hemispherical at both ends or heads. If the length of cylindrical part is zero, then the formula will calculate the volume inside spherical tank or ball shaped tank.
Use only measurements inside the tank, especially if the tank with a thick skin materials.
a = radius of sphere = half (½) diameter cylindrical
h = depth of liquid in the tank
L = length of cylindrical part of the tank
D = diameter of the cylindrical tank