Because castellated beams have many benefits in both engineering and economics, their application is growing daily. Space and lightweight are always important considerations, in addition to saving space by allowing large pipes, ducts, etc. to pass through the opening, utilizing of a castellated beam will help lessen the weight of the steel. However, these holes could severely limit the beam's ability to support loads, putting the beam in danger. Stiffeners surrounding the openings provide strength to the castellated beam. Therefore, a nonlinear numerical analysis is carried out in this study using ANSYS to study the effect of change in compactness for castellated beams, and the effect of various stiffener patterns (boundary, sleeve, horizontal, and vertical) on ultimate load of various compactness castellated beams to assess the effectiveness of the stiffeners placed around the openings. The findings demonstrated that beams with compact sections proved to be more successful to castellate than beams with non-compact and slender sections. Since the load capacity of slender castellated beams increases by 50% and 43% when stiffened by vertical, boundary, or sleeve stiffeners, respectively. Stiffening the slender castellated beams is more effective than non-compact ones. It is inefficient to stiffen compact castellated beams since doing so adds weight even while it increases load capacity by 10%. For cases of slender and non-compact specimens, the failure mode altered from web post buckling (W.P.B.) to flexural failure when stiffened by the boundary or sleeve stiffeners are used. Nevertheless, the horizontal stiffeners are unable to change the mode failure.