Forced expiratory volume (FEV) measures how much air a person can exhale during a forced breath. The amount of air exhaled may be measured during the first (FEV1), second (FEV2), and/or third seconds (FEV3) of the forced breath.

Forced vital capacity (FVC) is the total amount of air exhaled during the FEV test.

Forced expiratory volume and forced vital capacity are lung function tests that are measured during spirometry. Forced expiratory volume is the most important measurement of lung function. It is used to:

• Diagnose chronic obstructive pulmonary disease (COPD). A person with COPD has a lower FEV1 result than a healthy person.
• See how well medicines used to improve breathing are working.
• Determine if lung disease is getting worse. Decreases in the FEV1 value may indicate the lung disease is getting worse.