How to Use Peak Flow Calculator
Enter age, height, sex, measured peak flow, and the measurement unit. The Peak Flow Calculator converts m³/s to L/min when needed, estimates a predicted PEF, and reports the measured value as a percent of predicted.
The color-zone interpretation follows common peak-flow teaching: green at roughly 80% or more, yellow at about 50-79%, and red below about 50%.
If a patient has a known personal best, that personal-best comparison may be more useful than a population prediction. This tool is best for quick reference and education.
Formula & Theory — Peak Flow Calculator
The Peak Flow Calculator uses the following formula or scoring rule:
percent predicted = measured PEF ÷ predicted PEF × 100
1 m³/s = 60000 L/minPeak expiratory flow measures the fastest airflow achieved during a forceful exhalation. Predicted values vary with age, height, and sex because airway size and lung mechanics vary across people.
Percent predicted turns the measured flow into a relative value. A measured 350 L/min can mean different things for a tall young adult and a shorter older adult.
The prediction equation used here is a simplified reference and does not replace spirometry, asthma action plans, or clinician-defined personal zones.
Use Cases for Peak Flow Calculator
The Peak Flow Calculator is useful in specific situations such as:
- converting peak-flow readings between L/min and m³/s
- teaching green-yellow-red peak-flow zones
- checking whether a diary entry is near a predicted reference
- discussing why height and age affect expected peak flow