FEV1 helps measure the progression of lung conditions such as chronic obstructive pulmonary disease (COPD) or asthma. FEV stands for forced expiratory volume, which is the air you exhale in 1 second. A low FEV1 suggests a breathing obstruction.

Having trouble breathing is a hallmark symptom of COPD. COPD causes air to get trapped in your airways, making it difficult for your lungs to exhale it all out. Asthma causes your airways to narrow, making it more difficult to breathe.

FEV1 is measured during a spirometry test, also known as a pulmonary function test, which involves forcefully breathing out into a mouthpiece connected to a spirometer machine.

Read on to learn what your FEV1 score can mean and how it’s used to diagnose COPD, asthma, or rarer types of lung diseases.

Healthy values for FEV1 vary from person to person. They’re based on standards for an average person of that age, race, height, and gender. Each person has a predicted FEV1 value.

You can get a general idea of your predicted value with a spirometry calculator. The Centers for Disease Control and Prevention (CDC) provides a calculator that lets you enter your details.

If you have already received a COPD or asthma diagnosis, your FEV1 score can help determine your condition’s stage. This is done by comparing your FEV1 score to the predicted value of those individuals similar to you without a lung condition.

Your doctor will calculate a percentage difference to compare your FEV1 score and predicted value. This percentage can help stage COPD.

According to the COPD GOLD guidelines from 2018:

GOLD stage of COPDPercentage of predicted FEV1 value
very severeless than 30%

For asthma, there are similar guidelines from the National Heart Blood and Lung Institute. They are:

Asthma stagePercentage of predicted FEV1 value

Your FEV1 score alone isn’t used to diagnose COPD or asthma. A diagnosis requires a calculation involving FEV1 and another breathing measurement called forced vital capacity (FVC). FVC measures the greatest amount of air you can forcefully breathe out after breathing in as deeply as possible.

If your doctor suspects you have a lung condition, they’ll calculate your FEV1/FVC ratio. This represents the percentage of your lung capacity you can expel in 1 second. The higher your percentage, the larger your lung capacity and the healthier your lungs.

Your doctor will likely diagnose COPD if your FEV1/FVC ratio falls below 70% of the predicted value. You are likely to get a diagnosis of asthma if your ratio falls below 80% of the predicted value.

Your doctor will also likely use a COPD assessment test (CAT). This is a set of questions that look at how COPD affects your life. The results of the CAT and your spirometry test will help establish the overall grade and severity.

Your doctor may also look at other criteria to make a diagnosis of either COPD or asthma. This includes taking your detailed history, including whether you smoke, have had occupational exposure to a chemical or pollutant, and more.

They may also do a physical exam and refer you to a chest X-ray or CT. Finally, they make look at how you respond to certain inhaled medications.

It can be useful to monitor FEV1 over time for both COPD and asthma.


COPD is a progressive condition. This means that over time, COPD will typically worsen. People experience varying levels of COPD decline. Your doctor will monitor your COPD with a spirometry test, usually once a year. They’ll monitor you to determine how quickly COPD and lung function are worsening.

Being aware of your FEV1 score can help you manage your COPD. Experts make recommendations for the care of COPD based on these results. Between spirometry tests, your doctor may recommend rechecking your FEV1 whenever you see changes in your COPD symptoms.

Besides breathing difficulty, symptoms of COPD include:

  • coughing that produces a lot of mucus from your lungs
  • wheezing
  • tightness in your chest
  • shortness of breath
  • decreased ability to exercise or carry out routine activities

In most people, COPD is caused by cigarette smoking, but it can also occur due to long-term exposure to lung irritants other than smoke. This includes exposure to air pollution, chemical fumes, cooking fumes, and dust.

Smokers may need to take more frequent spirometry tests because they’re more likely to experience faster and more frequent changes in lung capacity than nonsmokers.

Learn the best apps to quit smoking.


In cases of asthma, your doctor may ask you to start using inhaled bronchodilator medications, after which they will want to recheck your FEV1 to see if your percentage improves.

Since asthma symptoms can be improved, if your second and subsequent spirometry readings show at least a 12% improvement, you are more likely to have asthma than COPD.

If there is no improvement, the doctor may try to switch your medications. If there is still no improvement, your doctor may suspect you have, in fact, a different condition like COPD.

Your doctor will also look at your symptoms to check for improvement. Asthma symptoms include:

  • coughing
  • chest tightness
  • breathing difficulty
  • speaking difficulty
  • fatigue

Asthma can be genetic or triggered by environmental factors like allergens. Some people do not experience breathing problems but only a chronic cough. This is known as couch-variant asthma. Some cases of severe asthma may also be difficult to treat.

FEV1 measures the stage of certain lung conditions like COPD and asthma. It indicates how much air you can exhale in one second, and a low FEV1 implies that your airflow is obstructed.

Your doctor will assess your FEV1/FVC ratio if they suspect you have a lung disorder, which helps them form a diagnosis. The larger the percentage, the healthier your lungs and airway are.