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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.

Enter Values

Age (years)

Height (cm)

Sex

Result

Enter values above and click Calculate to see your result.

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Formula

Core Formula

Gregg and Nunn Equations (Reference values)

How it works: 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

50 year old Male, 180cm -> ~600 L/min predicted.

Peak Expiratory Flow and Asthma Zones

Peak Expiratory Flow (PEF) measures the fastest rate at which you can blow air out of your lungs. It is a simple, portable test that helps monitor asthma control and detect early airway obstruction.

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.

Peak Expiratory Flow Rate: Asthma Zone Chart

Traffic light system for interpreting peak flow readings relative to your personal best. Used for daily asthma self-management and action plan decisions.

Zone	PEF Range	Symptoms	Action
Green	80-100% of personal best	No symptoms, breathing is good	Continue current treatment plan
Yellow	50-80% of personal best	Cough, wheeze, chest tightness, or nighttime symptoms	Use rescue inhaler, consider increasing controller medication, contact doctor if no improvement
Red	Below 50% of personal best	Severe shortness of breath, rescue inhaler not helping	Medical emergency: use rescue inhaler immediately, seek emergency care

Note: Establish your personal best PEF during a 2 to 3 week period when asthma is well controlled. Measure PEF at the same time each day, before taking medication. A drop of 20% or more from your personal best may indicate worsening asthma even before symptoms appear. Normal predicted PEF ranges: adult males 500-700 L/min, adult females 380-500 L/min (varies by age and height). For educational reference only.

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.

Can I use this Predicted Peak Flow Calculator on my own web page?

You can. Look for the "Embed" button near the top of this calculator. It lets you pick a size, border style, and color palette, then gives you an iframe tag to paste into any webpage. The widget is responsive, loads fast, and costs nothing. More details at calculory.com/services/embed-calculators.

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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