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 children (age 5–17), the calculator uses the European (Quanjer et al.) reference equations: males PEFR = (((height/100) × 6.14) − 0.043 × age − 0.432) × 60; females PEFR = (((height/100) × 4.93) − 0.015 × age + 0.040) × 60.

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 80, predicted values are shown but should be interpreted cautiously as fewer data points underpin the equations at extreme ages.

Predicted Peak Flow Calculator

Name: Predicted Peak Flow Calculator
Availability: InStock
Author: Nham Vu

Enter age, sex, and height to get the predicted normal peak expiratory flow rate (PEFR) for adults (Nunn & Gregg) and children (European reference).

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

Enter age, sex, and height to get the predicted normal peak expiratory flow rate (PEFR) for adults (Nunn & Gregg) and children (European reference).

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

Establish a personal best PEFR baseline for asthma management plans.
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: 2026-07-24 · Reviewed by Nham Vu