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Peak Flow Calculator

Health

Estimate predicted peak expiratory flow rate (PEFR) from height, age, and sex. Track your own peak flow meter readings for real monitoring over time.

Reviewed by the thecalcu.com team · Last updated July 20, 2026

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Predicted Peak Flow

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This calculator computes your Predicted Peak Flow from the values you enter.

Inputs
HeightAgeSex
Outputs
Predicted Peak Flow

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.

Why Use a Peak Flow Calculator?

Understanding how height, age, and sex generally relate to expected peak flow values is a useful educational starting point, especially for students and anyone new to respiratory self-monitoring concepts. This calculator applies a simplified reference formula instantly.

Who Should Use This Calculator?

  • Students of respiratory physiology or nursing learning how predicted peak flow is estimated.
  • People new to peak flow monitoring wanting general educational context before starting personal tracking.
  • Educators demonstrating the relationship between height, age, sex, and predicted peak flow.
  • Anyone curious about typical peak flow reference ranges.

What Insights Does the Peak Flow Calculator Give You?

The Predicted Peak Flow in litres per minute is the sole output, calculated from your entered height, age, and sex using a simplified reference formula, useful as general educational context, not a substitute for your own peak flow meter readings.

How to use this Predicted Peak Flow calculator

  1. Enter your height in centimetres.
  2. Enter your age.
  3. Select your sex.
  4. Read the Predicted Peak Flow instantly.
  5. 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.
Show formula & methodology ↓Show less ↑

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

What is peak expiratory flow rate (PEFR)?
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.
How is predicted peak flow calculated?
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.
Is this calculator a substitute for my personal peak flow meter readings?
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.
Why does peak flow generally decrease with age?
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.
Why does height affect predicted peak flow?
Taller individuals generally have larger airways and lung volumes, which tends to correlate with higher peak expiratory flow rates in reference population data.
How often should peak flow be measured for asthma monitoring?
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.
What does a peak flow reading below predicted mean?
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.
How accurate is this predicted formula compared to official nomograms?
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.
How does this relate to the FEV1/FVC Ratio Calculator?
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.
What unit is peak flow measured in?
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
predicted peak expiratory flow ratePEFR calculatorpeak flow meter referenceasthma peak flow calculator