A normal lung function value depends on a person's age, sex and height and can also depend on a person's race and weight, notes WebMD.com. A lung function test is conducted using a spirometer, which measures how well the lungs hold and exhale air. The values are expressed as a percentage of the expected value.
A lung function test is considered normal if the value falls within the expected range for a person with healthy lungs, notes WebMD.com. Patients should check with their physicians to determine what is considered a normal range for them. Values that fall out of the normal range may indicate the presence of some type of lung disease.