Spirometry measures how much air your lungs can hold and how fast you can move the air in and out. Spirometry testing takes place in a doctor's office, medical clinic, laboratory, or hospital. To perform this test, you will be asked to breathe into a sanitary tube as hard as you can and for as long as you can. The technician will explain the test to you and let you practice a few times to help you become comfortable. Sometimes these tests are repeated after using asthma medications in order to see how well the airway blockage can be reversed with medication. Spirometry numbers are ones that you will hear a lot over your lifetime with asthma.

  • The maximum amount of air you can force out after your greatest inhalation, called forced vital capacity, or FVC for short
  • The amount of air you can exhale in the first second of your greatest effort, called forced expiratory volume in 1 second, or FEV1 for short

To find out if you have blocked airways, your doctor looks for:


  • FEV1 less than values predicted for your height and age
  • FEV1/FVC less than 80% predicted

This means that with moderate asthma the total amount of air that you are able to exhale in 1 second compared to the total amount of air capacity possible is less than 80% of what is predicted for you. People who have mild asthma or no asthma have an FEV1/FVC that is equal to or greater than 80% or 0.80.

Your doctor will look at your spirometry readings both with and without the effect of medicine. Spirometry measurements taken after you inhale asthma medicine will let your doctor know if the airway limitations can be reversed with treatment. Your test values are compared to other people your same age, gender, and height, as well as to your own previous personal readings.

Written by Karen Serrano, MD

Emergency Medicine resident at the University of Wisconsin-Madison.

Reviewed by Lisa V. Suffian, MD

Instructor of Clinical Pediatrics in the Division of Allergy and Pulmonary Medicine at Saint Louis Children's Hospital, Washington University School of Medicine

Assistant Clinical Professor in the Department of Pediatrics at Cardinal Glennon Children's Hospital, Saint Louis University

Board certified in Allergy and Immunology

Last updated June 2008