Objectives Intravaginal rings (IVRs) are being developed as multipurpose prevention technologies for simultaneous HIV and pregnancy prevention. No empirical data exists to support the current 54-58mm external diameter (ED) as ideal. Understanding the impact of ED on IVR use is critical for developing products that are acceptable, facilitating comfortable, correct use. Methods We conducted a randomized, open-label, three-way crossover trial comparing adherence, preference, and acceptability of three non-medicated silicone IVRs of differing EDs (46 mm, 56 mm, 66 mm) each used continuously for ~30 days among 24 heterosexual couples in Atlanta, GA and Bronx, NY. We conducted in-depth interviews with women after study exit to explore their experiences with IVR use overall and by size. Interviews were recorded, transcribed, coded, and analyzed using MAXQDA. Results IVR use was highly acceptable, overall, with most participants preferring the 46mm or 56mm IVRs. Preference was influenced by ease of use (insertion/removal), experience/sensation using the IVRs (eg, comfort, not feeling the IVR, IVR staying in position and not interfering with sex). Many participants were surprised by how comfortable the IVRs were, sharing that acceptability was higher after study participation compared to initial pre-use concerns More participants reported adherence challenges with the largest (66 mm) IVR due to greater awareness of the IVR, issues with IVR placement, and discomfort during sex that led to IVR removals. Conclusions IVR acceptability and adherence were influenced by Ed. Given preferences for different sizes, developers should consider creating IVRs of different sizes to meet different users’ needs, while prioritizing IVRs with EDs ranging from 46 mm-56 mm.