Abstract A number of definitions with clear physical significance regarding the “average bond angles” (nonlinear case) are presented. Simple expressions of the average angles in terms of the linear and quadratic mean values of the displacements in the internuclear distances are given. The differences in the various average angles for H2O, D2O, CH4, CD4 and SO2 are estimated by means of a normal-coordinate analysis. The differences are shown to be small fractions of one degree. The root-mean-square angles for linear molecules (HCN, DCN, CO2 and CS2) are also calculated.