Lung Capacity Calculator
Enter the four basic lung volumes measured during spirometry to see Total Lung Capacity (TLC), Vital Capacity (VC), Inspiratory Capacity (IC), and Functional Residual Capacity (FRC) calculated instantly. Switch to Predicted mode to get your predicted FVC and FEV1 based on age, sex, and height using the Hankinson 1999 NHANES III reference equations - the same reference used in most clinical spirometry software.
What are lung volumes and capacities?
The respiratory system uses two layers of measurement. Lung volumes are the four primary subdivisions of the air space: Tidal Volume (TV), the volume moved during quiet breathing; Inspiratory Reserve Volume (IRV), the extra air you can inhale above a normal breath; Expiratory Reserve Volume (ERV), the additional air you can force out after a normal exhale; and Residual Volume (RV), air that remains even after a maximal exhalation and cannot be expelled. Lung capacities are combinations of two or more of these four volumes. Total Lung Capacity (TLC) is the sum of all four, representing the absolute maximum your lungs can hold. Vital Capacity (VC) is TLC minus RV, so it is everything you can actively move. Inspiratory Capacity (IC) is how much you can inhale from the resting end-expiratory level. Functional Residual Capacity (FRC) is the volume left in the lungs at the end of a normal passive exhale, where lung recoil and chest wall expansion forces balance each other.
How to use the volumes mode
Enter the four primary volumes obtained from pulmonary function testing. Typical adult defaults (IRV 3.0 L, TV 0.5 L, ERV 1.1 L, RV 1.2 L) produce a TLC of 5.8 L - squarely within the normal adult range. The calculator then works out TLC, VC, IC, and FRC instantly. All four inputs are in litres. Note that residual volume cannot be measured by conventional spirometry. It requires helium dilution, nitrogen washout, or body plethysmography. If you only have spirometry data (FVC, FEV1), use the Predicted mode instead to estimate your expected lung function from your demographics.
How to use the predicted FVC and FEV1 mode
Switch to Predicted mode and enter your age (18-80), sex, and height. The calculator applies the Hankinson 1999 NHANES III equations to compute the predicted forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) for someone of your demographic. These equations were derived from a large, healthy, non-smoking U.S. population and are widely used in clinical spirometry software. Optionally enter your measured FVC and FEV1 from a real spirometry test. You will then see percent-predicted values and your actual Tiffeneau-Pinelli index (FEV1/FVC ratio). An FEV1/FVC ratio below 70% alongside other findings may indicate airflow obstruction, while low FVC with a normal ratio can suggest restriction - but interpretation always requires clinical judgment and comparison with established lower limits of normal.
What the FEV1/FVC ratio tells you
The Tiffeneau-Pinelli index, FEV1 divided by FVC, is one of the most clinically important spirometry metrics. In healthy adults the ratio is typically 75-85% (above 70% is broadly normal). A ratio below 70% in the context of symptoms raises concern for obstructive lung disease such as asthma or COPD. In obstructive disease both FEV1 and VC may be reduced, but FEV1 falls disproportionately because airways resist flow. In restrictive disease (pulmonary fibrosis, obesity, neuromuscular weakness) both FVC and FEV1 shrink together, so the ratio often stays normal or even rises. Severity classification by FEV1 percent-predicted is used in GOLD staging for COPD: above 80% is mild (GOLD 1 if obstruction is confirmed), 50-79% is moderate (GOLD 2), 30-49% is severe (GOLD 3), and below 30% is very severe (GOLD 4).
Normal ranges for lung volumes and capacities (adults)
| Parameter | Abbreviation | Typical adults (L) | Formula |
|---|---|---|---|
| Tidal Volume | TV | 0.4 - 0.6 | measured |
| Inspiratory Reserve Volume | IRV | 2.0 - 3.5 | measured |
| Expiratory Reserve Volume | ERV | 0.7 - 1.2 | measured |
| Residual Volume | RV | 1.0 - 1.5 | measured (not by spirometry) |
| Vital Capacity | VC | 3.5 - 5.0 | IRV + TV + ERV |
| Inspiratory Capacity | IC | 2.5 - 4.0 | IRV + TV |
| Functional Residual Capacity | FRC | 1.8 - 2.4 | ERV + RV |
| Total Lung Capacity | TLC | 4.5 - 7.0 | IRV + TV + ERV + RV |
Approximate reference ranges. Actual normal values depend on age, sex, height, and ethnicity. Sources: West Respiratory Physiology, Wikipedia Lung Volumes.
Frequently asked questions
What is the difference between lung volume and lung capacity?
Lung volumes are the four indivisible air compartments: tidal volume (TV), inspiratory reserve volume (IRV), expiratory reserve volume (ERV), and residual volume (RV). Lung capacities are derived values that combine two or more of these volumes - for example, total lung capacity is the sum of all four, and vital capacity is the sum of IRV, TV, and ERV. Think of volumes as the building blocks and capacities as the composites.
Can I measure residual volume at home?
No. Residual volume is the air that cannot be exhaled, so it cannot be captured by breathing into a device. It must be measured indirectly using helium dilution (breathing a known concentration of helium and measuring dilution), nitrogen washout (breathing pure oxygen and measuring the nitrogen washed out), or body plethysmography (a sealed chamber that measures pressure changes during breathing). These tests are performed in specialized pulmonary function labs.
What is a normal FEV1/FVC ratio?
For most adults, an FEV1/FVC ratio above 70% is considered normal. The ratio naturally declines with age: a healthy 25-year-old might have a ratio around 80%, while a healthy 65-year-old might be around 70-72%. Values below 70% (or below the age-specific lower limit of normal) alongside reduced FEV1 and compatible symptoms suggest obstructive airway disease such as asthma or COPD.
How do age and height affect lung capacity?
Lung capacity is strongly related to height because taller people have larger thoracic cages. Predicted FVC and FEV1 increase roughly with the square of height in the NHANES III reference equations. Age has the opposite effect: lung function peaks in the mid-20s and then declines gradually, with FVC and FEV1 falling about 20-30 mL per year in healthy non-smokers. Sex also matters, as men typically have 25-30% larger lung volumes than women of the same height and age.
What does it mean if my TLC is elevated?
A TLC above the upper limit of normal (usually above 120% predicted) is called hyperinflation or air trapping. It is commonly seen in obstructive diseases such as emphysema, where destroyed alveolar walls lose their elastic recoil and airways collapse during exhalation, trapping extra air. The lungs effectively inflate more than normal at rest. Hyperinflation is associated with breathlessness, particularly on exertion, and a barrel-shaped chest on examination.
What does a reduced TLC mean?
A TLC below the lower limit of normal (usually below 80% predicted) suggests restriction. Causes include pulmonary fibrosis (stiff, scarred lung tissue), pleural disease, chest wall abnormalities such as kyphoscoliosis, respiratory muscle weakness, and significant obesity. A restrictive pattern on spirometry usually shows reduced FVC with a preserved or elevated FEV1/FVC ratio - but TLC measurement by body plethysmography is required to confirm true restriction.
Are these predicted values accurate for my ethnicity?
The Hankinson 1999 equations used here were developed from White (Caucasian), African American, and Mexican American populations in the NHANES III study. The calculator uses the White equations as a general reference. Lung function reference values differ meaningfully by ethnicity: on average, African American populations have predicted FVC and FEV1 values about 12% lower than White populations at the same age and height, and South and East Asian populations have values roughly 8-10% lower. Clinically, race-specific or ethnicity-neutral GLI-2012 equations are preferred for accurate interpretation.
Sources
- Hankinson JL, Odencrantz JR, Fedan KB. Spirometric reference values from a sample of the general U.S. population. Am J Respir Crit Care Med 1999;159:179-187.
- Quanjer PH et al. Multi-ethnic reference values for spirometry for the 3-95-yr age range: the Global Lung Function 2012 equations. Eur Respir J 2012;40:1324-1343.