Acute calculous cholecystitis (ACC) is a prevalent surgical emergency characterized by inflammation of the gallbladder, typically due to cystic duct obstruction by a gallstone. The diagnostic process relies on a combination of clinical assessment, blood investigations, and imaging modalities. Leukocytosis and elevated inflammatory markers like C.Reactive protein (CRP) are commonly seen in this condition, and ultrasound is the most common imaging modality used to diagnose acute calculus cholecystitis. The Tokyo Guidelines (TG) have served as a critical, internationally recognized framework for standardizing the diagnosis and severity grading of ACC, undergoing revisions in 2013 (TG13) and 2018 (TG18) to enhance specificity and accuracy. This review outlines the key diagnostic methods for acute calculus cholecystitis, focusing on the evolution of the Tokyo Guidelines criteria, the role of specific blood investigations, and the utility of various imaging modalities.