BACKGROUND Annular measurements traditionally guide transcatheter heart valve sizing in transcatheter aortic valve replacement (TAVR). Although supra-annular assessment has emerged as a crucial consideration, particularly in bicuspid aortic valve (BAV) cases, current measurement methods lack standardization and reproducibility. OBJECTIVES The aim of this study was to develop and validate a standardized multiplanar approach for transcatheter heart valve sizing integrating both annular and supra-annular measurements. METHODS This retrospective study included 377 patients (191 with BAVs,186 with tricuspid aortic valves [TAVs]) who underwent TAVR with the Venus A-Valve. The multiplanar protocol used measurements at 2-mm intervals above the annulus, incorporating both commissural and leaflet margin assessments. A subset of 54 patients underwent detailed postprocedural morphologic and biomechanical analyses. Clinical outcomes were compared with a propensity-matched cohort (n = 98 pairs) from the VENUS-A study using traditional annulus-based sizing. RESULTS The multiplanar strategy resulted in downsizing for 89.0% of BAV patients (170 of 191) and 64.5% of TAV patients (120 of 186) compared with annulus-based sizing. There were no significant differences between downsized and nondownsized cases in both the TAV and BAV groups. Postoperative analyses showed strong correlations between preprocedural measurements and postimplantation valve morphology and biomechanics. The multiplanar strategy group had a lower incidence of valve-in-valve procedures compared with the annulus-based group (3.1% vs 12.2%; P = 0.032; OR: 3.9; 95% CI: 1.206-16.186). CONCLUSIONS Multiplanar supra-annular measurement provides a comprehensive evaluation of aortic root anatomy, enabling more precise TAVR sizing for both BAV and TAV patients. (c) 2025 Published by Elsevier on behalf of the American College of Cardiology Foundation.