Total lung capacity (TLC) is the maximum volume of air that the lungs can hold upon the maximum effort of inspiration. Among healthy adults, the average lung capacity is about 6 liters. However, TLC can vary depending on age, gender, body composition, ethnicity, and certain respiratory diseases. TLC rapidly increases from birth to adolescence and plateaus at around 25 years old. Males tend to have a greater TLC than females, while individuals with tall stature tend to have greater TLC than those with short stature, and individuals with a high waist-to-hip ratio generally have a lower TLC. Clinicians can measure lung capacity by plethysmography, dilutional helium gas method, nitrogen gas washout method, or radiographically by a relatively new technique using computed tomography (CT). Methodically, the TLC is calculated by measuring the lung capacities: inspiratory capacity (IC), functional residual capacity (FRC), and the vital capacity (VC). TLC can be further divided into the following lung volumes: tidal volume (TV), inspiratory reserve volume (IRV), expiratory reserve volume (ERV), and the residual volume (RV).