Ask a medical professional for a definition of expiratory reserve volume (ERV) and they’ll offer something along the lines of: “The extra volume of air that can be expired from the lungs with determined effort following a normal tidal volume expiration.”

Let’s make that easier to understand.

Picture yourself sitting normally and breathing as you do when you are not exerting yourself or exercising. The amount of air you breathe in is your tidal volume.

After you breathe out, try to exhale more until you are unable to breathe out any more air. The amount of air you can force out after a normal breath (think about blowing up a balloon) is your expiratory reserve volume.

You can tap into this reserve volume when you exercise and your tidal volume increases.

To sum up: Your expiratory reserve volume is the amount of extra air — above a normal breath — exhaled during a forceful breath out.

The average ERV volume is about 1100 mL in males and 800 mL in females.

Respiratory volumes are the amount of air inhaled, exhaled, and stored in your lungs. Along with expiratory reserve volume, some terms that are often part of a ventilatory pulmonary function test and can be helpful to know include:

  • Tidal volume. The amount of air you typically breathe into your lungs when at rest and not exerting yourself. The average tidal volume is about 500 mL for both men and women.
  • Inspiratory reserve volume. The amount of extra air inhaled — above tidal volume — during a forceful breath in. When you exercise, you have a reserve volume to tap into as your tidal volume increases. The average inspiratory reserve volume is about 3000 mL in males and 2100 mL in females.
  • Vital capacity. The total usable volume of the lungs that you can control. This is not the entire lung volume as it is impossible to voluntarily breathe all of the air out of your lungs. The average vital capacity volume is about 4600 mL in males and 3400 mL in females.
  • Total lung capacity. The total volume of your lungs: your vital capacity plus the amount of air you cannot voluntarily exhale. The average total lung capacity volume is about 5800 mL in males and 4300 mL in females.

If your doctor sees signs of a chronic lung condition, they will use spirometry to determine how well your lungs work. Spirometry is an important diagnostic tool for identifying:

Once diagnosed with a chronic lung disorder, spirometry might be used to monitor progress and to determine if your breathing problems are being properly treated.

The amount of lung capacity varies from person to person based on their physical makeup and their environment.

You are likely to have a larger volume if you:

  • are tall
  • live at a higher altitude
  • are physically fit

You are likely to have a smaller volume if you:

Your expiratory reserve volume is the amount of extra air — above-normal volume — exhaled during a forceful breath out.

Measured with spirometry, your ERV is part of the data gathered in pulmonary function tests used to diagnose restrictive pulmonary diseases and obstructive lung diseases.