Lung Capacity Calculator

Lung capacity describes several distinct volumes rather than one measurement. Vital capacity is the greatest volume that can be exhaled after a maximal inhalation. Forced vital capacity measures a similar volume during a forceful maneuver. Total lung capacity includes vital capacity plus residual volume, the air remaining after maximal exhalation. Spirometry can measure vital capacity and airflow but cannot directly measure residual volume or total lung capacity; those usually require body plethysmography, gas dilution, or another specialized method. This calculator uses simple adult reference equations based on height, age, and sex. The male equation estimates liters as 0.052 times height in centimeters minus 0.022 times age minus 3.60. The female equation uses 0.041 times height minus 0.018 times age minus 2.69. It then provides a rough total lung capacity estimate by treating vital capacity as 80 percent of total capacity. That final relationship is an approximation, not a replacement for measured static lung volumes. Predicted values depend strongly on the reference population. Modern pulmonary laboratories commonly use Global Lung Function Initiative equations that incorporate age, height, sex, and ancestry-related reference strategy across broad age ranges. Interpretation should use z-scores and lower limits of normal rather than a single universal percent cutoff. Technique, posture, effort, calibration, recent illness, bronchodilator use, and equipment quality can all affect a measured result. Biological sex in the displayed historical equation refers to the equation category, and a pulmonary specialist can choose the most appropriate reference for an individual. A reduced vital capacity can occur with restriction, air trapping, submaximal effort, neuromuscular weakness, chest wall conditions, obesity, or prior lung surgery. A normal estimate cannot rule out asthma, emphysema, interstitial lung disease, or other respiratory conditions. Symptoms including severe shortness of breath, blue discoloration, chest pain, confusion, or rapidly worsening breathing require urgent medical assessment. Use this educational estimate to understand terminology or check arithmetic. Do not use it to diagnose disease, assess fitness for surgery, alter respiratory treatment, or interpret a home spirometer without a qualified clinician and a complete pulmonary function report.