Peak flow meter

A peak flow meter is a small plastic device with a measuring gauge along the side, which measures how fast you can blow air out of your lungs.

People with asthma can use the meter to get baseline measurements of their normal peak flow, which can then be used to:

  • help monitor their condition
  • assess how well asthma medicine is working
  • assist in self-management (knowing what to do when your asthma flares up - this is shown by low peak flow readings).

What does a peak flow measurement tell us?

The speed and force that you can blow air out of your lungs depends on how open your airways are.

  • If you are well, the airways are open and your peak flow reading is high.
  • If the airways are tight, such as when your asthma is playing up, your peak flow reading will fall.

A peak flow meter will tell you how well your lungs are functioning. However, it is not a standalone tool and it should be used in conjunction with the following symptom assessment:

  • are you sleeping through the night and not waking with asthma symptoms?
  • are you using your reliever inhaler more than three times a week?
  • is asthma stopping you from doing your usual activities?

When should I use a peak flow meter?

Initially, you should take your peak flow readings before using your inhalers every morning and again in the evening, for two weeks. Your doctor can then see if your values are as high as they should be. (Peak flow calculator - MD+CALC) You may choose to either make a graph or keep a diary (Asthma & Respiratory Foundation of NZ) of these readings and how you feel.

  • If your peak flow values are high, your doctor may tell you to reduce your medication.
  • If your peak flow values are low, your doctor may change your medication or increase the number of puffs you are taking.
  • If your treatment is altered, it is important to keep using your peak flow meter to monitor any changes.

When you are well and your peak flow reading is at its best and steady, you won't have to use your meter every day.

Peak flow meters should be used when:

  • you have a runny nose or feel a cold coming on
  • you just don't feel as well as usual
  • you know you've been exposed to one of your asthma triggers (e.g. something that makes asthma worse)
  • your treatment has been changed
  • you have had a recent acute asthma attack (keep recording until readings are normal and symptoms stabilise)
  • before you visit your doctor.

What is a normal peak flow reading?

Your doctor, practice nurse or asthma educator (health professional) can work out what your peak flow reading should be, based on your height, age and gender. 

Peak flow charts & tools

What are the benefits of using a peak flow meter?

  • It helps you to identify asthma symptoms and triggers.
  • You can find out if your asthma treatment is having the effect that it should.
  • Your peak flow diary is a record you can show the doctor on the next visit, especially if you are not as well as usual.
  • When used with your self management plan, it means that you are in control of your asthma.

How do I use a peak flow meter?

  • Sit upright or stand up.
  • Slide the marker on the peak flow meter to the zero by the mouthpiece end (as far as it will go).
  • Hold the meter level and keep your fingers from obstructing the marker.
  • Take a deep breath in.
  • Put the meter in your mouth and close your lips tight around the mouthpiece, making a good seal.
  • Keep your tongue away from the mouthpiece.
  • Blow the air out of your lungs as hard and fast as you can, with a strong huff.
  • Note your reading from the marker level.
  • Repeat these steps two more times.
  • Record the highest of the 3 readings.
  • If you find that your first blow is always the best, then you only need to blow once.
  • Ask your doctor, nurse or asthma educator to check you are using the meter correctly.

What to do if your readings are down

Ask your doctor to write you a self management plan, which tells you what to do if your readings drop and your asthma symptoms increase. If you follow your plan and your readings still keep dropping, see your doctor.

Learn more

Asthma in Children Ministry of Health NZ, 2014
Asthma management tools The Asthma & Respiratory Foundation (NZ)
Asthma - Symptoms, Management, Treatment Southern Cross Healthcare Group, 2013

Credits: Original material provided by The asthma foundation NZ. Latest update by Health Navigator April 2016.