Peak Flow Calculator
Calculate estimated peak expiratory flow and assess respiratory function
Patient Details
Range: 5-100 years (calculator most accurate for ages 15-75)
Average: Adult males ~175 cm (5'9" / 69"), females ~162 cm (5'4" / 64")
Note: Ethnicity affects expected values due to physiological differences
Peak Flow Results
Formula Used:
Male: (5.2 × height) - (0.13 × age) - 108
Height in cm, age in years
Measured Peak Flow (Optional)
Diurnal Variability (Optional)
⚠️ Medical Disclaimer: This calculator is for educational purposes only. Peak flow measurements should be interpreted by qualified healthcare professionals. Always consult your doctor for asthma management and treatment decisions.
Peak Flow Zones
Green Zone (≥80%)
All clear - continue normal activities
Yellow Zone (50-79%)
Caution - take rescue medication
Red Zone (<50%)
Emergency - seek immediate help
Normal Values
Usage Tips
Measure at the same time daily
Take three readings, use the highest
Stand up straight when measuring
Blow as hard and fast as possible
Understanding Peak Expiratory Flow
What is Peak Expiratory Flow?
Peak expiratory flow (PEF) is the maximum speed of air during forced expiration. It measures how well air moves out of your lungs and is particularly useful for monitoring asthma and other respiratory conditions.
When to Measure PEF
- •Moderate to severe asthma monitoring
- •After medication changes
- •Occupational asthma assessment
- •Daily respiratory function tracking
Factors Affecting PEF
- Age: Decreases with aging
- Height: Taller individuals have higher values
- Gender: Males typically have higher values
- Ethnicity: Variations due to lung anatomy
- Physical fitness: Better fitness = higher PEF
- Time of day: Usually lowest in early morning
Important: Personal best values are more reliable than estimated values for ongoing monitoring. Track your own patterns over time.
How to Use a Peak Flow Meter
Preparation
- Stand up straight
- Reset the meter to zero
- Take the deepest breath possible
- Place lips tightly around mouthpiece
Measurement
- Blow as hard and fast as possible
- Record the reading
- Reset and repeat 2 more times
- Use the highest of three readings