π« Lung Capacity Estimator
Predicted vital capacity from the Baldwin equations.
For informational purposes only, not medical advice. Consult a healthcare professional.
Vital capacity, the most air you can exhale after a full breath in, is predicted from age, sex, and height because lungs scale with body size and shrink with age. The Baldwin equations give the expected value in liters: taller people have bigger lungs, and capacity falls roughly 20 to 30 mL per year after the mid-20s. Spirometry results are read as percent of predicted, with 80% the usual normal cutoff.
Enter age, sex, and height for the predicted vital capacity, and optionally your measured VC from spirometry to see the percent of predicted. This estimates VC only; full lung volumes and flow rates need formal pulmonary function testing.
How to Use This Calculator
Enter age, sex, and height in centimeters. If you have spirometry results, enter the measured vital capacity in liters to get percent of predicted. Read the predicted value and the comparison band. Values under 80% of predicted deserve pulmonary follow-up, especially with symptoms.
Enter age, sex, and height.
Optionally enter your measured VC from spirometry.
Read the predicted VC in liters.
Compare as percent of predicted against the 80% normal cutoff.
The Baldwin Equations
Women: VC (mL) = (21.78 - 0.101 x age) x height (cm)
Baldwin, Cournand, and Richards published these regressions in 1948 from measurements on healthy subjects, and they remain in use because they are simple and roughly right. The age term captures the steady decline of chest wall compliance and respiratory muscle strength; the height term captures thoracic size. Modern reference equations (GLI, NHANES III) refine predictions by ethnicity and use more complex models, so treat Baldwin as a solid estimate rather than the final word. Percent of predicted, not the raw liters, is what clinicians interpret.
Worked Example
A 40-year-old man, 175 cm: predicted VC is 4.05 L. A spirometry reading of 3.6 L is 89% of predicted, landing in the Normal (>=80% predicted) range. Taller, younger, and male all raise the prediction; a 65-year-old woman at 160 cm predicts about 2.6 L.
Reading Percent of Predicted
At or above 80% of predicted is normal. Sixty to 79% is mildly reduced, 40 to 59% moderately reduced, and under 40% severely reduced. A low VC with a normal FEV1/FVC ratio suggests restriction (stiff lungs or chest wall); a low ratio suggests obstruction (asthma, COPD). Single VC numbers never diagnose: pattern across the full spirometry panel plus imaging and history does.
Breathlessness Deserves Testing
New or worsening shortness of breath, wheezing, or chronic cough should be evaluated with proper spirometry, not estimated from a calculator. Home peak flow meters track asthma day to day but do not replace formal testing. For informational purposes only, not medical advice. Consult a healthcare professional.
Related tools: lung nodule growth rate, mean airway pressure and BMI calculator.
For informational purposes only, not medical advice. Consult a healthcare professional.
Frequently Asked Questions
What is normal lung capacity?
Predicted vital capacity depends on age, sex, and height: roughly 3 to 5 liters for adults. Results are read as percent of predicted, with 80%+ normal.
Does lung capacity decrease with age?
Yes, about 20 to 30 mL per year after the mid-20s, from chest wall stiffening and weaker respiratory muscles.
Can you increase lung capacity?
Exercise improves how well you use capacity and strengthens respiratory muscles, but total lung volume is largely set by body size. Wind players and swimmers show modest gains.
What is the difference between VC and TLC?
Vital capacity is the usable exhale volume; total lung capacity adds the residual volume you cannot exhale. VC is measured by simple spirometry, TLC needs body plethysmography.
Why is percent predicted more useful than liters?
Because a 3-liter VC is normal for a small older woman and reduced for a tall young man. Percent of predicted adjusts for body size.
Does smoking reduce vital capacity?
Smoking accelerates the age-related decline and causes obstruction that lowers usable volumes. Quitting slows the decline toward the normal aging rate.
What causes a restrictive pattern?
Pulmonary fibrosis, chest wall disease, neuromuscular weakness, and obesity can all reduce VC with a preserved FEV1/FVC ratio.
Are the Baldwin equations still used?
They remain reasonable estimates, but modern labs use GLI or NHANES III reference equations that account for ethnicity with more data.
Why does predicted lung capacity fall with age?
The chest wall stiffens, the diaphragm weakens, and lung tissue loses some elastic recoil over the decades. The Baldwin equations bake this in: predicted VC drops roughly 20 to 30 mL per year after the mid-20s. An 80-year-old is expected to have about a liter less vital capacity than the same person at 30, and that is normal aging, not disease.
My measured VC is 75% of predicted. Should I worry?
It deserves follow-up but not panic. Under 80% of predicted is the standard flag for a restrictive pattern, but a single spirometry effort can read low from poor technique, a recent cold, or testing too soon after bronchodilator use. Repeat the test properly and pair it with flow measurements (FEV1) before drawing conclusions.