Lung Capacity Calculator
Calculate TLC, vital capacity, inspiratory capacity, and FRC from IRV, TV, ERV, and RV spirometry values.
What Is Lung Capacity?
Lung capacity describes the maximum volume of air the lungs can hold and the subdivisions measured during spirometry and body plethysmography. Understanding how inspiratory reserve volume (IRV), tidal volume (TV), expiratory reserve volume (ERV), and residual volume (RV) combine helps clinicians assess restrictive and obstructive lung disease. For nodule malignancy risk on screening CT, see the Lung Nodule Growth Rate Calculator.
How Lung Volumes Are Calculated
From the four component volumes, this calculator derives four composite capacities: total lung capacity (TLC = IRV + TV + ERV + RV), vital capacity (VC = IRV + TV + ERV), inspiratory capacity (IC = IRV + TV), and functional residual capacity (FRC = ERV + RV). All values are expressed in liters or milliliters.
Clinical Context
Reduced VC may indicate restrictive disease, while an elevated RV relative to VC suggests air trapping in obstructive conditions such as COPD. TLC requires RV measurement, which typically needs body plethysmography or helium dilution rather than simple spirometry alone. Always interpret results alongside predicted values for age, sex, and height.
Frequently Asked Questions
What is total lung capacity (TLC)?
TLC is the maximum volume of air contained in the lungs after a maximal inspiration. It equals the sum of all four lung volume compartments: IRV, TV, ERV, and RV.
What is the difference between VC and IC?
Vital capacity (VC) is the maximum volume that can be exhaled after a full inspiration, excluding RV. Inspiratory capacity (IC) is the volume that can be inspired above the resting FRC level (IRV plus TV).
What is functional residual capacity (FRC)?
FRC is the volume of air remaining in the lungs at the end of a normal passive expiration. It equals ERV plus RV and represents the equilibrium point of the respiratory system at rest.
Can I enter volumes in milliliters?
Yes. Use the unit toggle to switch between liters and milliliters. The calculator converts all inputs internally and displays results in your selected unit.
What are normal adult lung volumes?
Typical adult TLC is approximately 6 L, though predicted values vary with height, sex, and age. TV at rest is about 0.5 L, IRV roughly 3 L, ERV about 1.2 L, and RV near 1.2 L in healthy adults.
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