**Ligand bond number** (LBN) represents the effective total number of ligands surrounding a metal center, M. More simply, it represents the number of coordination sites occupied on the metal. Based on the Covalent Bond Classification method, the equation for LBN is as follows:

LBN = L + X + Z

On comparison to the classical coordination number, some major differences can be seen. For example,(η^{5}–cyclopentadienyl)_{2}Cr (ML_{4}X_{2}) and (η^{6}–benzene)_{2}Cr (ML_{6}) both have a LBN of 6 as compared to classical coordination numbers of 10 and 12. Well known complexes such as Ferrocene and Uranocene also serve as examples where LBN and coordination number differ. Ferrocene has two η^{5} cyclopentadienyl ligands while Uranocene has two η^{8} cyclooctatetraene ligands; however, by covalent bond classification the complexes are found to be ML_{4}X_{2} and ML_{6}X_{4}. This corresponds to LBN values of 6 and 10 respectively, even though the total coordination numbers would be 10 and 16. The usefulness of LBN to describe bonding extends beyond just sandwich compounds. Co(CO)_{3}(NO) is a stable 18-electron complex in part due to the bonding of the NO ligand in its linear form. The donation of the lone pair on the nitrogen makes this complex ML_{4}X, containing 18 electrons. The traditional coordination number here would be 4, while the CBC more accurately describes the bonding with a LBN of 5. In simple cases, the LBN is often equal to the classical coordination number (ex. Fe(CO)_{5}, etc.)

LBN for transition metals trends downward as you move right across the periodic table. This trend is highlighted in the LBN plots of Groups 3 through 10. Groups exhibit trends, but the LBN for individual complexes can vary.