The significance of teachers' self-efficacy in coding education within K-12 settings has grown substantially. However, the literature lacks subject-specific measurement tools tailored to assess teachers' self-efficacy in coding instruction. This study adopted a mixed methods approach to develop a reliable and valid instrument for measuring computer science (CS) teachers' self-efficacy in teaching coding. The scale development involved a rigorous process encompassing item generation, expert validation, and pilot testing. Importantly, this process unfolded in seven steps with two distinct phases, and each phase involved independent sample groups. Subsequently, a comprehensive survey was administered to two samples of CS teachers (n = 318, n = 295) to assess the scale's psychometric properties. The results revealed robust internal consistency and construct validity of the 20-item Coding Teaching Self-Efficacy Scale (CTSES) with four intercorrelated dimensions: student motivation, subject knowledge, classroom management, and material development. Furthermore, additional analyses revealed the significant impact of teaching experience and self-reported coding knowledge level on teachers' self-efficacy in teaching coding. The implications of this study hold significance for both practitioners and researchers to understand teachers' self-efficacy in teaching coding and to explore its relation to teacher training, curriculum development, and the broader advancement of coding education within school settings.