Put the pointer on the gauge of the peak flow meter to 0 or the lowest number on the meter. In the photograph, this is about 50.

Attach the mouthpiece to the peak flow meter. Some meters don't have a separate mouthpiece.

While standing, take a deep breath.

Put the peak flow meter mouthpiece in your mouth, and close your lips tightly around the outside of the mouthpiece. Don't put your tongue inside the mouthpiece.

Breathe out as hard and as fast as you can for 1 or 2 seconds. A hard and fast breath usually produces a "huff" sound.

Check the number on the gauge, and write it down. This is your peak expiratory flow (PEF). In the photograph above, the PEF is about 180.