Lung capacity
 
If you experience breathing problems, there are a number of tests your doctor may perform to decide what is causing your symptoms. One way is to assess your peak flow. This will help your doctor identify and manage any breathing problems over time and ensure that, if necessary, you receive the relevant treatment or that any treatment you are already on is still working. 
 
Peak flow test measures 
This test measures the air flow in litres per second as you breathe out. Your doctor will ask you to breathe out as hard as you can into the mouthpiece of a test meter. 
 
Knowing your numbers 
Peak flow readings will vary for every person. It depends on your age, height and gender. So it is difficult to say exactly what your best peak flow should be. Here are some average examples of peak flows: 
 

• 635 litres per minute for a 25 year old man, who is 6'1" (1.85m) tall. 
   
  
• 465 litres per minute for a 40 year old woman, who is 5'2" (1.75m) tall. 
   
  
• 300 litres per minute for a child between 6-15 years old and 4'7" (1.40m) tall.

 
Your doctor or practice nurse will advise you about your specific peak flow reading, what the results might mean for you and, if you need to repeat the peak flow tests, how often you should do so.