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    Estimated/Expected Peak Expiratory Flow (Peak Flow)

    Quantifies asthma exacerbation severity.
    When to Use
    Why Use

    Use in patients age 5-80 years with asthma.

    • Useful in patients who do not know their baseline peak expiratory flow rate (peak flow).

    • Comparison of a patient’s current peak flow to a known or expected personal best is only one aspect of the evaluation of a child with an acute asthma exacerbation. Other important factors such as respiratory rate, lung auscultation, mental status, and accessory respiratory muscle use must also be considered.

    • Height and sex have been the factors most strongly correlated with peak flow across multiple studies; however, other differences, including ethnicity and other factors may also play a role in affecting predicted values.

    Asthma exacerbation severity can be quantified by comparing a patient’s current peak expiratory flow rate (PEFR) to their most recent personal best value. In the absence of a known recent personal best, this calculator can be used to estimate an expected “personal best.” The difference between the predicted and actual value can therefore help the clinician determine how severe the current exacerbation is.



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    Next Steps
    Creator Insights


    Patients with much lower actual peak flow than estimated typically require further treatment of their asthma.

    Critical Actions

    Assessment of peak flow must not delay administration of critical treatments for acute asthma exacerbations.


    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).

    Facts & Figures


    Variability Peak flow zone
    >80% Green
    50-80% Yellow
    <50% Red


    Dr. John L. Hankinson

    About the Creator

    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

    Content Contributors
    Reviewed By
    • Josh Needleman, MD
    About the Creator
    Dr. John L. Hankinson
    Content Contributors
    Reviewed By
    • Josh Needleman, MD