Calculate Estimated/Expected Peak Expiratory Flow Rate

Peak expiratory flow rate (PEFR) is the maximum flow rate (expressed in liters per minute [L/min]) generated during a forceful exhalation, starting from full inspiration.


Interpretation of the Peak Flow Variability:
Variability Peak flow zone
>80% Green
50-80% Yellow
<50% Red



Ages 5-7 years and any ethnicity:

PEFR = [(Height, cm - 100) × 5] + 100

Ages 8-80 years and Caucasian, African American, or Mexican American ethnicity:

See regression equations in Tables 4-5 in Hankinson 1999 (NHANES III).

Ages 8-17 years, all other ethnicities:

PEFR = [(Height, cm - 100) × 5] + 100

Ages 18-80 years, all other ethnicities:

PEFR, male = {[(Height, m × 5.48) + 1.58] - [Age × 0.041]} × 60

PEFR, female = {[(Height, m × 3.72) + 2.24] - [Age × 0.03]} × 60

Peak flow variability:

Peak flow variability, % = (actual peak flow rate / estimated peak flow rate) x 100

This calculator uses the equations from Hankinson 1999 (NHANES III) where available, and equations from Knudson 1983 where there are deficits in the data (patients not 8-80 years and Caucasian, African American, or Mexican American ethnicity).



Dr. John L. Hankinson

John L. Hankinson, PhD, is a biomedical engineer and consultant. He is also the course director for a National Institute for Occupational Safety and Health approved spirometry course and serves on the ATS Proficiency Standards for Pulmonary Function Laboratories Committee. Dr. Hankinson’s primary research is focused on respiratory diseases and spirometry.
To view Dr. John L. Hankinson's publications, visit PubMed