Lung Capacity Calculator
Calculate your total lung capacity (TLC), vital capacity (VC), inspiratory capacity (IC), and functional residual capacity (FRC) from spirometry lung volume measurements including IRV, TV, ERV, and RV with charts.
About This Calculator
The Lung Capacity Calculator computes your total lung capacity (TLC), vital capacity (VC), inspiratory capacity (IC), and functional residual capacity (FRC) from four lung volume measurements obtained during a pulmonary function test (spirometry). This tool is designed for healthcare professionals, respiratory therapists, and individuals tracking their lung health.
Lung capacities are derived by combining different lung volumes. Total lung capacity (TLC) is the sum of inspiratory reserve volume (IRV), tidal volume (TV), expiratory reserve volume (ERV), and residual volume (RV): TLC = IRV + TV + ERV + RV. Vital capacity (VC) represents the maximum air that can be exhaled after a deep inhalation: VC = IRV + TV + ERV. Inspiratory capacity (IC) is the maximum volume that can be inhaled from resting expiration: IC = IRV + TV. Functional residual capacity (FRC) is the air remaining in the lungs during normal breathing: FRC = ERV + RV.
Regional Notes
India: Pulmonary function tests in India typically follow ATS/ERS guidelines. Spirometry is widely available in major hospitals. Normal reference values for the Indian population differ from Western standards due to ethnic and anthropometric differences — the Indian Council of Medical Research (ICMR) provides region-specific reference equations.
United States: The American Thoracic Society (ATS) recommends race-specific reference equations for spirometry interpretation. The Global Lung Function Initiative (GLI-2012) equations are commonly used across the US for calculating predicted lung capacity values.
United Kingdom: The British Thoracic Society (BTS) follows ATS/ERS guidelines for pulmonary function testing. UK laboratories predominantly use the GLI-2012 reference equations, which account for age, height, sex, and ethnicity to provide accurate predicted values.
Frequently Asked Questions
How is total lung capacity (TLC) calculated?
Total lung capacity (TLC) is calculated by adding all four lung volumes: inspiratory reserve volume (IRV) + tidal volume (TV) + expiratory reserve volume (ERV) + residual volume (RV). The normal range for TLC in adults is 5 to 7 liters.
What is the difference between vital capacity and total lung capacity?
Vital capacity (VC) is the volume of air that can be exhaled after a maximum inhalation, calculated as IRV + TV + ERV. Total lung capacity (TLC) includes the residual volume as well (IRV + TV + ERV + RV), representing the complete air volume in the lungs.
What are normal lung capacity values?
Normal lung capacity values vary by age, sex, height, and ethnicity. TLC typically ranges from 5 to 7 liters. VC ranges from 3 to 5 liters. IC ranges from 2 to 4 liters. FRC is approximately 2 liters. These values decrease with age and are generally higher in males and taller individuals.
What lung volumes are needed for this calculator?
You need four lung volume measurements from spirometry: inspiratory reserve volume (IRV), tidal volume (TV), expiratory reserve volume (ERV), and residual volume (RV). These are typically measured during pulmonary function testing.
What does functional residual capacity (FRC) indicate?
Functional residual capacity (FRC) is the volume of air remaining in the lungs during normal relaxed breathing, calculated as ERV + RV. A normal FRC is around 2 liters. Increased FRC may indicate hyperinflation seen in COPD, while reduced FRC can indicate restrictive lung disease.
What is the difference between lung volumes and lung capacities?
Lung volumes are directly measured by spirometry and include IRV, TV, ERV, and RV. Lung capacities are combinations of two or more lung volumes: TLC (all four), VC (IRV+TV+ERV), IC (IRV+TV), and FRC (ERV+RV).
How does age affect lung capacity?
Lung capacity peaks around age 20-25 and naturally declines with age. The decline is approximately 20-30 mL per year after age 30. Factors like smoking, pollution exposure, and respiratory conditions can accelerate this decline.
Can I use this calculator before a pulmonary function test?
This calculator is designed to compute lung capacities from existing spirometry measurements. For predicted (expected) vital capacity values based on age, sex, and height, use a vital capacity prediction equation. Always consult a healthcare professional for interpretation of your lung function results.