Following generalization can be easily derived for various types of lattice arrangements in cubic cells between the edge length (a) of the cell and r the radius of the sphere. For simple cubic : a = 2r or r =
a
2
For body centred cubic : a =
4
√3
r or r =
√3
4
a For face centred cubic : a = 2√2r or r =
1
2√2
a Thus the ratio of radii of spheres for these will be simple: bcc: fcc =