Peak Flow Calculator
HealthEstimate predicted peak expiratory flow rate (PEFR) from height, age, and sex. An educational reference estimate — track your own peak flow meter readings for real monitoring.
Predicted Peak Flow
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What is a Predicted Peak Flow?
The Peak Flow Calculator estimates predicted peak expiratory flow rate (PEFR) from height, age, and sex, using a simplified educational reference formula. It provides a general population estimate, not a personalized clinical reading.
For real asthma monitoring, use an actual peak flow meter and track against your own personal best, as recommended by most respiratory health guidance. For related lung function tools, see Lung Capacity Calculator and FEV1/FVC Ratio Calculator.
How to use this Predicted Peak Flow calculator
- Enter your height in centimetres.
- Enter your age.
- Select your sex.
- Read the Predicted Peak Flow instantly.
- For actual asthma monitoring, use a real peak flow meter and establish your own personal best reading, then track against that baseline as advised by your healthcare provider.
Formula & Methodology
Male: Predicted PEFR = (Height in cm × 3.2) + 40 − (Age × 1.5) Female: Predicted PEFR = (Height in cm × 2.7) + 25 − (Age × 1.5) Worked example — a 35-year-old man, 175 cm tall: Predicted PEFR = (175 × 3.2) + 40 − (35 × 1.5) = 560 + 40 − 52.5 = 547.5 L/min
Frequently Asked Questions
Peak expiratory flow rate is the maximum speed of air a person can forcefully exhale after a full inhalation, commonly measured using a handheld peak flow meter and often used by people with asthma to monitor their lung function over time.
This calculator uses a simplified reference formula based on height, age, and sex, reflecting the general relationship that taller, younger individuals typically have higher peak flow rates.
No — for real asthma monitoring, health authorities generally recommend establishing your own personal best peak flow using an actual peak flow meter and tracking against that personal baseline, rather than relying on a predicted population estimate like this calculator.
Lung elasticity and respiratory muscle strength generally decline gradually with age in adults, which is reflected in most predicted peak flow reference formulas showing a downward adjustment as age increases.
Taller individuals generally have larger airways and lung volumes, which tends to correlate with higher peak expiratory flow rates in reference population data.
Monitoring frequency depends on individual asthma management plans set by a healthcare provider — some people check daily, others only during symptom flare-ups; this calculator doesn't provide personalized monitoring guidance.
A reading below predicted or below your personal best can be a sign worth discussing with your healthcare provider, but interpretation should always be done by a qualified professional as part of your broader asthma or respiratory management plan, not from this calculator alone.
This calculator uses simplified, illustrative coefficients for general educational purposes and is not the official clinical nomogram used in medical practice — official peak flow prediction charts used by healthcare providers may give somewhat different reference values.
Both are lung function reference tools, but the [FEV1/FVC Ratio Calculator](/fev1-fvc-ratio-calculator/) works from actual measured spirometry values, while this calculator predicts an expected peak flow from height, age, and sex alone.
Peak flow is measured in litres per minute (L/min), the standard unit used on peak flow meters and in respiratory reference charts.
Also known as