Lung Volume Calculator
Calculate lung volumes: tidal volume, vital capacity, and functional residual capacity. Understand FEV1/FVC ratio for obstructive vs restrictive lung disease patterns.
🏃 Physiology📐 VC = IRV + TV + ERV🧬 Biology
Tidal volume TV (L)
Inspiratory reserve volume IRV (L)
Expiratory reserve volume ERV (L)
Residual volume RV (L)
Please enter valid values.
Formula & Reference
| Variable | Symbol | Formula | Units |
|---|---|---|---|
| Lung Volume Calculator | — | VC = IRV + TV + ERV | liters |
Step-by-Step Examples
Example 1
Normal Adult Male
TV=0.5, IRV=3.0, ERV=1.2, RV=1.2 L.
- VC = 0.5+3.0+1.2 = 4.7 L
- TLC = 4.7+1.2 = 5.9 L
- FRC = 1.2+1.2 = 2.4 L
- Typical healthy adult male
✓ VC=4.7L, TLC=5.9L (normal adult male)
Example 2
Obstructive Disease
Emphysema: TV=0.5, IRV=2.5, ERV=0.8, RV=2.5 L.
- VC = 3.8 L (reduced)
- TLC = 6.3 L (increased — air trapping)
- RV/TLC ratio elevated
- FEV1/FVC < 0.7 expected
✓ TLC increased, air trapping
Example 3
Restrictive Disease
Fibrosis: TV=0.4, IRV=1.8, ERV=0.8, RV=1.0 L.
- VC = 3.0 L (reduced)
- TLC = 4.0 L (reduced)
- All volumes proportionally reduced
- FEV1/FVC may be normal or high
✓ All volumes reduced — restrictive pattern
Real-World Applications
Pulmonology
Lung volumes diagnose obstructive vs restrictive disease and monitor progression.
Exercise Physiology
Ventilatory reserve and breathing mechanics during exercise.
Anesthesia
Lung volumes determine ventilator settings for mechanically ventilated patients.
Clinical Research
Pulmonary function tests are primary endpoints in COPD and IPF trials.
Common Mistakes to Avoid
⚠️
RV cannot be measured directly
Residual volume requires plethysmography or gas dilution — it cannot be obtained by spirometry alone. Simple spirometry gives VC, not TLC.
⚠️
Not standardizing to predicted values
Lung volumes depend on height, age, sex, race. Always compare to predicted normal using reference equations.
⚠️
Confusing FVC with VC
FVC (forced vital capacity from spirometry) may be less than slow VC in obstructive disease due to dynamic compression. Both measurements have clinical utility.
Frequently Asked Questions
What is tidal volume? ▾
Volume of air per normal breath at rest. Normal: 400-600 mL (0.4-0.6 L). Increases to 1-2 L during heavy exercise.
What is vital capacity? ▾
Maximum air exhaled after maximum inhalation = IRV + TV + ERV. Normal male: 4-5 L. Female: 3-4 L. Reduced in restrictive disease.
What is FEV1/FVC ratio? ▾
FEV1 = air exhaled in first second. FVC = total exhaled. Ratio <0.7 defines airflow obstruction (COPD, asthma). Normal: >0.7-0.75.
What is air trapping? ▾
Increased RV and RV/TLC ratio due to obstruction. Trapped air cannot be exhaled. Occurs in COPD, emphysema. Leads to barrel chest appearance.
What is the difference between COPD and asthma? ▾
COPD: irreversible obstruction, emphysema/chronic bronchitis. Asthma: reversible obstruction, bronchospasm. Both show FEV1/FVC <0.7 during obstruction.