Definitions & Nornal Values

Normal Values

  • Normal values for each data point obtained during spirometry is derived from a predictive equation and is patient specific. The predictive equations require the patient’s gender, height, weight, and age. Some predictive equations also include race.
  • Fortunately, nearly all modern spirometers automatically calculate the patient’s predicted values.
  • The data point is generally considered normal if it falls within 80% to 120% of what has been predicted.


Total Lung Capacity (TLC) The maximum amount of air the lung can hold.
Vital Capacity (VC) The maximum amount of air that can be exhaled following a maximum inhalation.
Forced Vital Capacity (FVC) The vital capacity obtained when the subject is blowing out as hard and fast as possible.
Residual Volume (RV) The amount of air remaining in the lungs following a maximum exhalation.
Functional Residual Capacity (FRC) The amount of air remaining in the lungs following a normal exhalation.

Authored by William A. French. Medically reviewed by Dr. Barbara Erickson, PhD, RN, CCRN.

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