Predicted Peak Flow Calculator
Estimate predicted Peak Expiratory Flow (PEF) based on age, height, and sex. Used for asthma action plan zones: green is above 80% of personal best, yellow is 50-80%, and red is below 50%. Essential for monitoring airway obstruction and treatment response.
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Result
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Formula
Uses standard regression data to provide a baseline for what a healthy individual of your profile should blow into a peak flow meter.
Worked Example
Peak Expiratory Flow and Asthma Zones
- Predicted PEF is calculated from age, sex, and height using published regression equations
- Green zone (above 80% of best): good control, continue regular treatment
- Yellow zone (50-80% of best): caution, increase medications or consult your action plan
- Red zone (below 50% of best): medical emergency, use rescue inhaler and seek care
- PEF should be measured at the same time each day for consistency, ideally morning and evening
PEF monitoring is most effective when used alongside a written asthma action plan developed with your healthcare provider. Record your readings daily and share trends at follow-up visits.
You can also calculate changes using our Minute Ventilation Calculator or PaO2/FiO2 Ratio Calculator.
Frequently Asked Questions
What is a normal peak flow?
It varies by age, height, and sex. Typical adult males have PEF of 500-700 L/min, while adult females typically range from 380-500 L/min. This calculator gives you a predicted baseline.
What is the Green Zone in an asthma action plan?
The green zone is 80-100% of your personal best or predicted PEF. It means your asthma is well controlled and you should continue your regular medications.
Why does height matter for peak flow?
Taller individuals generally have larger lungs and higher peak flow rates. Height is one of the strongest predictors of PEF alongside age and sex.
What do the Yellow and Red zones mean?
Yellow zone (50-80% of best) indicates caution, meaning your asthma is not well controlled and you may need to adjust medications. Red zone (below 50%) is a medical alert requiring immediate bronchodilator use and medical attention.
Does peak flow change with age?
Yes. PEF typically peaks in the late 20s to early 30s and gradually declines with age due to reduced lung elasticity and respiratory muscle strength.
Should I use predicted PEF or personal best?
Personal best is preferred for asthma action plans because it reflects your individual lung capacity. Predicted values serve as a reference when a personal best has not yet been established through consistent monitoring.
Medical Disclaimer
This calculator is provided for informational and educational purposes only. It is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making any decisions based on these results. Do not disregard or delay seeking medical advice because of information obtained from this tool.
AI Assistant
Ask about this calculator
I can help you understand the predicted peak flow calculator formula, interpret your results, and answer follow-up questions.
Try asking
Our AI assistant provides general estimates and advice only. Please consult a qualified healthcare professional before making any health-related decisions.
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