This study investigates the optical separation of mechanical strain and charge doping in graphene using Raman spectroscopy. The authors found that the effects of strain and charges can be separated by correlation analysis of the G and 2D Raman modes, allowing for the simple quantification of both. Graphene sheets on silica substrates exhibit in-plane strain ranging from -0.2% to 0.4%, which is relieved and becomes compressive upon thermal treatments. The study suggests that substrate-mediated mechanical strain is a common phenomenon in two-dimensional materials and provides a useful method for characterizing graphene-based materials and devices. The proposed analysis method is based on the linear relationship between the frequency shifts of the G and 2D modes under strain and charge doping, with the strain-sensitivity of these modes being well characterized. The results highlight the importance of considering both strain and charge effects in the interpretation of Raman spectra of graphene and other two-dimensional materials.This study investigates the optical separation of mechanical strain and charge doping in graphene using Raman spectroscopy. The authors found that the effects of strain and charges can be separated by correlation analysis of the G and 2D Raman modes, allowing for the simple quantification of both. Graphene sheets on silica substrates exhibit in-plane strain ranging from -0.2% to 0.4%, which is relieved and becomes compressive upon thermal treatments. The study suggests that substrate-mediated mechanical strain is a common phenomenon in two-dimensional materials and provides a useful method for characterizing graphene-based materials and devices. The proposed analysis method is based on the linear relationship between the frequency shifts of the G and 2D modes under strain and charge doping, with the strain-sensitivity of these modes being well characterized. The results highlight the importance of considering both strain and charge effects in the interpretation of Raman spectra of graphene and other two-dimensional materials.