Peak Expiratory Flow Calculator

yr
cm
L/min
Health

Calculate predicted peak expiratory flow (PEF) based on age, height, and sex. Used in asthma management.

Formula

Wright/Nunn-Gregg equations for predicted PEF by age, height, sex. Zone = actual/predicted × 100%
  • Green zone ≥80% predicted: continue regular medications.
  • Yellow zone 50–79%: step up therapy, possible oral steroids.
  • Red zone <50%: emergency — bronchodilators, call doctor/emergency services.
  • Always use personal best PEF (not predicted) after establishing baseline over 2–3 weeks.

35-year-old male, 175 cm, measured 480 L/min

Inputs
  • Sex: male
  • Age: 35 yr
  • Height: 175 cm
  • Actual Peak Flow (measured): 480 L/min

Predicted ≈ 600 L/min. 480/600 = 80% → Green zone.

Frequently asked questions

How do I use a peak flow meter?
Stand up, take a deep breath, place meter in mouth (lips sealed around mouthpiece), blast out as fast and hard as possible. Record the number. Repeat 3 times, use the best reading.