Ab-dependent cellular cytotoxicity (ADCC) responses are of growing interest in the HIV vaccine field but current cell-based assays are usually difficult to reproduce across laboratories. We developed an ELISA and multiplex assay to model the cross-linking of Fcg receptors (FcgR) by Abs, which is required to initiate an ADCC response. Our FcgR dimer ELISA readily detected Abs in samples from two separate cohorts of the partially efficacious Thai RV144 HIV vaccine efficacy trial. The FcgR dimer-binding Abs induced by the RV144 regimen correlated well with a functional measure of ADCC as well as IgG subclasses. The highthroughput multiplex assay allowed us to simultaneously measure FcgR dimer-binding Abs to 32 different HIV Ags, providing a measure of the breadth of FcgR-binding Abs induced by the RV144 trial. FcgR-binding Abs specific to V regions 1 and 2 were strongly associated with increased breadth of recognition of different Env proteins, suggesting anti-V regions 1 and 2 Abs may be a marker of ADCC breadth. This FcgR dimer provides an important tool for the further analysis and refinement of ADCCinducing HIV and other antiviral vaccine regimens.