Rigorous evidence generation with randomized controlled trials (RCTs) has lagged for aneurysmal subarachnoid hemorrhage (SAH) compared to other forms of acute stroke. Besides its lower incidence compared to other stroke subtypes, the presentation and outcome of SAH patients also differ. This must be considered and adjusted for in designing pivotal RCTs of SAH patients. Here, we show the effect of the unique expected distribution of the SAH severity at presentation (World Federation of Neurological Surgeons, WFNS, grade) on the outcome most used in pivotal stroke RCTs (modified Rankin Scale, mRS) and consequently on the sample size. Further, we discuss the advantages and disadvantages of different options to analyze the outcome and control the expected distribution of WFNS grades in addition to showing their effects on the sample size. Last, we offer methods that investigators can adapt to more precisely understand the effect of common mRS analysis methods and trial eligibility pertaining to the WFNS grade in designing their large-scale SAH RCTs.