This work analyzes the angular resolution (AR) of the monostatic forward-looking synthetic aperture radar (FL-SAR). A general mathematical expression for the theoretical AR of the FL-SAR is derived. Simulation-based validations show that the proposed expression yields precise ARs for both single input single output FL-SAR (FL-SISO-SAR), and multiple input multiple output FL-SAR (FL-MIMO-SAR) configurations. Moreover, the proposed expression shows compatibility with near-field as well as far-field geometries. Lastly, the proposed expression also covers challenging situations such as FL-MIMO-SAR with largely spaced MIMO arrays and targets at look angles equal or close to zero degree.