Wall climbing robots (WCRs) are deployed to perform tasks like cleaning windows of multistoried buildings, surveillance in areas where human faces difficulty, painting high raised walls, cleaning inner surfaces of huge boilers in industries etc. For all these purposes, the WCRs need to move in terrains and surfaces that are rough and uneven. There is a high possibility that a WCR can tip over such uneven surfaces and this might be an important issue of concern. Factors such as force and moment have a greater effect on stability. Modeling the stability of the WCR with respect to force and moment would be helpful to avoid tip-overs. This paper proposes an angle-force-moment based stability criteria suitable for standalone WCRs. A suction chamber based WCR has been considered for deriving the stability margin, SMWCR. When θ goes beyond 15 degrees, SMWCR drops below 1.98. There is a fair chance that the WCR would topple down beyond the tip-over axis at this θ. This stability margin not only helps in knowing the angular stability of the WCR but also avoids path deviation. The deviation of stability margin with respect to change in suction force and frictional force has been studied. © 2020 IEEE.