Peak Expiratory Flow Rate (PEFR) Calculator
Estimate your predicted peak flow and compare it to your current reading for asthma management.
What is Peak Expiratory Flow Rate?
The Peak Expiratory Flow Rate (PEFR) is a measurement of how fast a person can exhale air from their lungs. This metric is a vital indicator of lung function, particularly for individuals managing obstructive airway conditions like asthma or chronic obstructive pulmonary disease (COPD).
How to Use This Calculator
This tool uses standardized regression equations (based on the Nunn and Gregg studies) to estimate what your normal peak flow should be based on your biological sex, age, and height. By entering your "Current Reading" from a hand-held peak flow meter, you can see where you stand relative to your predicted baseline.
Understanding the Peak Flow Zones
- Green Zone (80% – 100% of predicted): Your breathing is well-controlled. Continue your standard maintenance medications.
- Yellow Zone (50% – 80% of predicted): Caution. Your airways are narrowing. You may need to use rescue medication or adjust your treatment plan as advised by your doctor.
- Red Zone (Below 50% of predicted): Medical Emergency. Seek immediate medical attention or follow your emergency asthma action plan.
Example Calculation
If a 40-year-old male is 180 cm tall, his predicted PEFR is approximately 610 L/min. If his current meter reading is 450 L/min, he is at roughly 74% of his predicted value, placing him in the Yellow Zone.
Tips for Accurate Measurement
To get the most accurate reading from your physical peak flow meter, ensure you are standing upright. Take as deep a breath as possible, place the mouthpiece in your mouth with a firm seal, and blow out as hard and fast as you can. Perform the test three times and record the highest of the three values.