The recent definitions on intra-abdominal pressure (IAP), intra-abdominal volume (IAV) and abdominal compliance (C ab ) are a step forward in understanding these important concepts. They help our understanding of the pathophysiology, aetiology, prognosis, and treatment of patients with low C ab . However, there is still a relatively poor understanding of the different methods used to measure IAP, IAV and C ab and how certain conditions may affect the results. This review will give a concise overview of the different methods to