Lung Capacity Estimator

Lung capacity (FVC) estimation predicts your Forced Vital Capacity, the maximum volume of air you can push out in a single hard breath, from age, height, and sex using standard spirometry reference equations.

Predicted FVC formulas (the European ECCS/ERS 1993 equations, Quanjer and colleagues):

Males:
FVC (liters) = (5.76 × Height in m) − (0.026 × Age) − 4.34

Females:
FVC (liters) = (4.43 × Height in m) − (0.026 × Age) − 2.89

This page used to call these the Knudson equations. They are not: Knudson’s 1983 set has different coefficients. These are the European Community for Steel and Coal equations, adopted by the European Respiratory Society in 1993 and printed on lab reports across Europe for twenty years. They were fitted to adults aged 18 to 70, roughly 155 to 195 cm for men and 145 to 180 cm for women, so outside that the answer is an extrapolation.

Height carries most of the weight in both, which is why a tall 60-year-old often has a larger FVC than a short 25-year-old. Age subtracts 26 mL a year, about a quarter of a liter per decade.

Important note: reference equations differ by population, and this matters more than people expect. Labs have been moving to the Global Lung Initiative equations, GLI-2012 and since 2023 the race-neutral GLI Global set, which cover ages 3 to 95. The 1993 equations are known to run a few hundred millilitres low for some groups, so the figure below can differ from a clinic report. Use it to understand the shape of the relationship, not to second-guess a spirometry result.

Predicted FVC by age and height, from the formulas above:

Reading a measured result. This is the part a doctor actually reads, and it needs a measured spirometry result as well as a predicted one. Enter yours below and the calculator works it out two ways.

The old rule is a fixed share of predicted: under 80% counts as low. It is still common, but it flags too many older people and too few young ones. Current ERS/ATS guidance (2022) uses the lower limit of normal instead, the level only the bottom 5% of healthy people fall below, and grades how far under it you are with a z-score:

For the 1993 equations the lower limit sits 1.00 L below predicted for men and 0.71 L below for women, and one z-score is 0.61 L for men and 0.43 L for women.

A low FVC on its own does not say why. Spirometry separates the two main patterns using the FEV1/FVC ratio: obstruction, as in asthma or COPD, empties slowly so the ratio falls below about 0.7, while restriction, as in fibrosis or obesity, holds less air but empties normally so the ratio stays normal or rises. This calculator does not estimate FEV1, so it cannot tell you which you have.

Worked example:

Male, 42 years old, 178 cm tall.
FVC = (5.76 × 1.78) − (0.026 × 42) − 4.34
FVC = 10.25 − 1.09 − 4.34 = 4.82 liters predicted

If spirometry measures 3.8 L: 3.8 ÷ 4.82 = 79% of predicted. The lower limit of normal is 4.82 − 1.00 = 3.82 L, and the z-score is (3.8 − 4.82) ÷ 0.61 = −1.67, so both rules call it a mild reduction, only just.

Factors that reduce FVC: smoking, obesity, scoliosis, neuromuscular disease, pulmonary fibrosis. Factors that go with a higher one: tall stature, being young, and swimming. Swimmers often test above predicted, partly because people with big lungs gravitate to the sport. Exercise does not change lung size much once you are grown, but not smoking keeps the yearly decline close to the 26 mL the equations assume.