To interpret the significance of peak expiratory flow measurements, a comparison is made to reference (normal, predicted) values based on measurements taken from the general population.
Various reference values have been published in the literature and vary by population, ethnic group, age, sex, height and weight of the patient.
For this reason, tables or charts are used to determine the normal value for a particular individual.
More recently, medical calculators have been developed to calculate predicted values for peak expiratory flow.
There are a number of non-equivalent scales used in the interpretation of peak expiratory flow.

Some examples of Reference Values are given below.
There is a wide natural variation in results from healthy test subjects.

Wright scale
EN 13826 or EU scale
NHANESIII reference values provided by the US Centers for Disease Control (CDC)
In 2004 the UK switched from the original Wright scale to the newer, more accurate European scale.
Wright values may be converted to the EU scale using the following formula:
The reverse calculation is:
Where  is the value in the Wright scale.

These formulas have also been trended over time in both rural and metropolitan areas both as air quality studies and as studies on asthma due to the Peak Flow measurement's accuracy as a predictor of mortality and poor prognosis.
To interpret the significance of peak expiratory flow measurements, a comparison is made to reference (normal, predicted) values based on measurements taken from the general population. Various reference values have been published in the literature and vary by population, ethnic group, age, sex, height and weight of the patient. For this reason, tables or charts are used to determine the normal value for a particular individual. More recently, medical calculators have been developed to calculate predicted values for peak expiratory flow. There are a number of non-equivalent scales used in the interpretation of peak expiratory flow.
Some examples of Reference Values are given below. There is a wide natural variation in results from healthy test subjects.
Wright scale
EN 13826 or EU scale
NHANESIII reference values provided by the US Centers for Disease Control (CDC)
In 2004 the UK switched from the original Wright scale to the newer, more accurate European scale. Wright values may be converted to the EU scale using the following formula:
The reverse calculation is:
Where  is the value in the Wright scale.
These formulas have also been trended over time in both rural and metropolitan areas both as air quality studies and as studies on asthma due to the Peak Flow measurement's accuracy as a predictor of mortality and poor prognosis.
Peak expiratory flow