Ultrasound measurements and normal values of the liver: a comprehensive review and practical guide.

Reliable and reproducible sonographic measurements are essential for accurate liver assessment, both in daily clinical practice and in research. Reference values enable clinicians to differentiate between physiological and pathological findings and thus support diagnostic accuracy, follow-up, and therapeutic decision-making. This comprehensive review synthesizes current evidence on normal liver size as assessed by ultrasound, with a particular focus on measurement techniques, standard values, anatomical variants, and the clinical contexts in which these parameters are relevant. Special attention is given to the influence of patient-related factors such as body constitution, sex, age, and ethnicity. The role of right, left, and caudate lobe measurements is discussed in detail, outlining their relevance in conditions such as hepatomegaly, vascular disorders, or post-resection follow-up. Limitations of currently available data are acknowledged, especially regarding interobserver variability and lack of global uniformity. Future priorities include the establishment of consensus-based international reference standards and the integration of emerging technologies, such as artificial intelligence and advanced image analysis tools, to enhance reproducibility, reduce variability, and improve clinical utility. Ultimately, standardized liver measurements should form an integral part of multiparametric ultrasound examinations to optimize patient care.