I have a pretty basic problem; I am trying to work out the extracellular volume fraction for a voxel containing cylinders that are closely packed in a hexagonal structure. My cylinders have a radius of 0.5 E-6 m and have a separation of 1.1 E-6 m I have been told that I can use the following formular to work this out; S=R sqrt(2pi/(f sqrt3))) where S is the seperation, R is the radius and f is the intracellular volume fraction, then of course 1-f will give me my desired value. However, this does not give a fraction. Can anyone help!

Many thanks