Which equation is used for adults?

For adults (age ≥ 18), the calculator uses the Nunn & Gregg (1989) regression equations: males PEFR = (((height/100) × 5.48) + 1.58 − (age × 0.041)) × 60; females PEFR = (((height/100) × 3.72) + 2.24 − (age × 0.030)) × 60. Height is in cm and age in years.

Which equation is used for children?

For ages 5–17, the calculator uses the pediatric height-based equation cited by the American Thoracic Society: ln(PEF in L/s) = −10.99 + 2.54 × ln(height in cm). The result is converted to L/min. Pediatric reference values vary by population and measurement method.

What does percent predicted mean?

Percent predicted = (measured PEFR / predicted PEFR) × 100. Values ≥ 80% are typically considered normal (green zone). 50–79% indicates mild-to-moderate impairment (yellow zone). Below 50% signals severe obstruction (red zone) and often requires immediate medical attention.

How accurate are these predictions?

Predicted values are population averages. Individual normal ranges vary; a personal best PEFR measured when the patient is well is often more clinically meaningful than the population prediction.

What age range does this cover?

This calculator covers ages 5–80. Below age 5 reliable PEFR effort is difficult and other spirometry references are preferred. Above age 80 is excluded because reference equations lack sufficient normative data for older adults.

Predicted Peak Flow Calculator

Enter age, sex, and height to estimate normal peak expiratory flow for adults with Nunn & Gregg or children with an ATS pediatric reference equation.

Patient Details

Sex

Male Female

Age (years, 5–80)

Height

Standing height in centimeters

Measured PEFR (L/min, optional)

Results

Enter details and click Calculate

Summary

Predicted peak flow (PEFR) is the maximum airflow rate during a forced exhalation, measured in liters per minute. This calculator uses the Nunn & Gregg equations for adults and the ATS pediatric height equation ln(PEF in L/s) = −10.99 + 2.54 × ln(height in cm) for children. A personal best measured while well is often more useful for an individual asthma action plan than a population prediction.

How it works

Select the patient's sex (male or female).
Enter the patient's age in years.
Enter standing height in centimeters or inches.
Click Calculate to get the predicted PEFR in L/min.
Compare the result to the patient's measured PEFR to determine percent predicted.
Use the percent predicted to guide asthma zone classification (green ≥80%, yellow 50–79%, red <50%).

Use cases

Provide a temporary reference benchmark when an individual personal best PEFR has not yet been established.
Determine percent predicted PEFR when evaluating asthma severity.
Monitor lung function trends over time in patients with obstructive lung disease.
Screen for airflow obstruction in occupational health assessments.
Educate patients about their expected normal range and action thresholds.
Cross-check spirometry results against population reference values.

Frequently Asked Questions

Last updated: 2026-06-15 · Reviewed by Nham Vu