Background Back-table bovine pericardial conduits may be fashioned for small-calibre arterial reconstruction when autologous vein is unavailable. Their final pressurised diameter cannot be assumed from nominal introducer sheath size. We evaluated a pragmatic intravascular ultrasound-based sizing method and developed the Stella Chart. Methodology Bovine pericardial conduits were fashioned around 7, 8, 10 and 12 Fr Cook introducer sheaths using continuous 6-0 polypropylene with locking knots at 1-cm intervals. Each construct was submerged in saline, statically pressurised to 150 mmHg and assessed using intravascular ultrasound at three predefined locations. Measured luminal diameter was compared with sheath outer diameter, and longitudinal dimensional variation was calculated. Results Twelve intravascular ultrasound measurements were obtained across four constructs. Mean luminal diameters for the 7, 8, 10 and 12 Fr constructs were 2.9, 2.9, 4.1 and 5.3 mm, respectively. Within-construct variation was 0.1–0.3 mm. Relative to sheath outer diameter, achieved conduit diameter differed by −0.1 mm for 7 Fr, −0.4 mm for 8 Fr, +0.1 mm for 10 Fr and +0.7 mm for 12 Fr. The 7 and 8 Fr constructs converged at approximately 2.9 mm, while the 12 Fr construct expanded beyond its mandrel diameter. Conclusion Nominal sheath size did not demonstrate a linear relationship with final pressurised conduit diameter. Intravascular ultrasound enabled direct back-table verification and identified size-dependent behaviour not predicted by geometric calculation alone. The Stella Chart provides an empirical framework for constructing small-calibre bovine pericardial conduits when standard options are unavailable.