There is herein provided a method for measuring the GOSNR that can be implemented using commercial-grade transceivers and which accounts for linear optical impairments (e.g. PMD, PDL and CD) and transceiver intrinsic impairments. The method may be implemented using an Optical Spectrum Analyzer (OSA) and either the system transceivers or other commercial-grade transceivers. The proposed measurement method is based on mixed optical and electronic technologies, using an OSA and a transceiver pair. By measuring a signal quality metric Qm and the OSNR under varied power and ASE noise conditions, a constant value RBW that relates the GOSNR to the signal quality metric Qm is derived. The GOSNR is then obtained from these results.