<p>Recognizing Chinese characters is a fundamental skill that is crucial for later reading development and basic educational achievement in China. However, there is currently a lack of published tests or norms that provide adequate feedback on children's character size development. To address this gap, we developed the Chinese character size test (CCST) for Mandarin Chinese students in grades 1–6. To address the need for resource-efficient assessment, longitudinal tracking precision, and curriculum-aligned interpretation, we applied rigorous test development processes, vertical test equating, and the item response theory framework to measure children’s character size development throughout primary grades. A comprehensive evaluation of the CCST's psychometric properties yielded satisfying results, including item statistics, test reliability, inferential score reliability, criterion-related validity, and empirical validity. Normative data from a representative sample of 7,459 primary school students in Beijing were analyzed to construct the norm-referenced and criterion-referenced character size scores. The results indicated that the mean character sizes of primary students in grades 1–6 were 1,227, 1,898, 2,422, 2,722, 2,932, and 3,060 characters, respectively, and that approximately 5.1% of the students in grades 3–6 failed to achieve the required character size level by the national curriculum criterion. In conclusion, the CCST is a child-friendly, highly interpretable, and open-access instrument with strong psychometric quality and comprehensive scoring feedback. This work would interest a wide range of users, including researchers, educators, and practitioners.</p>