Volumetric assessment of the liver is essential for planning safe hepatectomy and minimizing the risk of posthepatectomy liver failure (PHLF). Advances in imaging and software have enabled precise measurement of liver volumes and improved evaluation of the future liver remnant (FLR). Standardized volumetric methods, taking into account body size, provide reliable cutoffs to guide resection strategies and identify patients at increased risk for PHLF. In addition, techniques such as portal vein embolization and kinetic growth rate assessment are crucial for optimizing liver regeneration in patients with insufficient FLR. This chapter reviews current approaches to liver volumetry, safe thresholds for hepatectomy in healthy and diseased livers, and the clinical implications of volumetric studies in modern hepatobiliary surgery.