AbstractThe authors discuss the structural rule of different kinds of polyhedral boranes and propose a general topological formula for calculating the number of bonding molecular orbitals. In the case of single polyhedral boranes, results obtained from the formula are the same as those from the famous Wade rule. Futhermore, the formula can also be used to calculate the number of bonding molecular orbitals of joined‐type polyhedral boranes. We have also made some quantum chemistry calculations to verify the concept that the number of bonding molecular orbitals of boranes can be determined by considering only the corresponding boron polyhedral framework