Peak Expiratory Flow (PEF)
Enter patient age, height, and measured peak flow to determine predicted values and control zones for asthma action plans.
Choose the unit reported by the peak flow meter.
Results
Predicted PEF
7881 L/min
Patient PEF
450 L/min
6% of predicted
Zone
Red zone: medical alert—seek immediate care.
Zonal action plan:
- Green (≥80%): continue routine maintenance therapy.
- Yellow (50–79%): adjust medications—use quick-relief inhaler, review controller adherence.
- Red (<50%): medical alert—consider systemic steroids and emergency evaluation.
How to Use This Calculator
Measure peak flow properly
Have the patient stand, inhale maximally, and exhale forcefully into the meter—repeat three times and record the best.
Enter demographics accurately
Age and height drive predicted values. Use consistent units and update as patients grow (children/adolescents).
Update asthma action plan
Use zone classification to guide therapy adjustments and patient education. Document thresholds in the action plan.
Formula
Male predicted PEF (L/min) = (Height(m) × 5.48 − Age × 0.041) × 1000.
Regression models from Nunn AJ, Gregg I. Thorax. 1989.
Frequently Asked Questions
How often should patients check peak flow?
Daily monitoring is recommended for moderate-to-severe asthma or during exacerbations.
What if predicted PEF is negative?
Regression equations may yield low values outside model ranges. Ensure age/height are within adult ranges (≥15 years). Use pediatric charts otherwise.
Can I enter values in L/s?
Yes—select L/s, and the calculator converts to L/min internally.
Are ethnicity-specific equations used?
This tool uses widely adopted Nunn & Gregg equations. Consider local reference values if available.
How do I set personalized zones?
Base zones on the patient’s personal best peak flow, not just predicted values. Use this calculator to guide initial expectations.