Packing Efficiency
The percentage of the total volume of a unit cell that is actually occupied by the constituent particles.
Formula / equation
(volume of atoms / cell volume) × 100
Unit
Dimensionless
In depth
Assuming hard spheres, packing efficiency is 52% for simple cubic, 68% for body-centred cubic and 74% for both close-packed arrangements — the mathematical maximum for identical spheres. Higher efficiency generally means greater density and stronger metallic bonding.
Examples in the real world
Copper's 74% packing gives a density of 8.96 g/cm³, well above sodium's 68%-packed 0.97 g/cm³.