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The formula-based estimation of the right internal jugular venous (IJV) catheterization depth can be inaccurate when using ultrasound guidance. External landmark-based and radiological landmark-based methods have been proposed as alternatives to estimate the insertion depth. This study aimed to evaluate these methods using transesophageal echocardiography (TEE)-guided insertion depth as the reference. Ninety-seven adult cardiac surgery patients underwent real-time ultrasound-guided right IJV catheterization, with placement at the superior vena cava-right atrium (SVC-RA) junction under TEE guidance. The primary outcome compared the accuracy of external-landmark and radiological-landmark methods in estimating optimal catheter position (2 cm above to 1 cm below the SVC-RA junction), while secondary outcomes assessed their reliability and agreement with TEE. The external-landmark method proved more accurate than the radiological-landmark method (91.8% vs. 68%, p < 0.001) and had a higher correlation with TEE (r = 0.83 vs. 0.67). Bland-Altman analysis showed a mean difference of 0.08 cm between external-landmark and TEE methods (limits of agreement: -1.75 to 1.90 cm) and 0.43 cm for radiological-landmark (limits of agreement: -2.63 to 3.49 cm). Overall, the external-landmark method is a reliable and simple technique for estimating right IJV catheter depth and is more useful in cardiac surgery compared to the radiological-landmark method.Trial registration Thai Clinical Trials Registry (TCTR20200410012). Date registered April 9, 2020., Competing Interests: Declarations. Competing interests: The authors declare no competing interests. Ethical approval: The study was conducted in accordance with the Declaration of Helsinki and was approved by the Institutional Ethics Board of the Research Ethics Committee of the Faculty of Medicine, Chiang Mai University (ANE-2562–06940) on March 27, 2020., (© 2025. The Author(s).)