CHEMISTRY CLASS 12, Chapter 1 Solid States Class 12 Chemistry, Chapter 1 Solid States | Page 30

Therefore, Packing efficiency =( Volume occupied by four spheres in the unit cell X 100)/( Total volume of the unit cell)
Efficiency of Packing in Body Centred Cubic Structures
The length of the body diagonal c = 4r, where r is the radius of the sphere as all the spheres along the diagonal touch each other. Therefore,