What’s Normal?

How do we know when the results from a Pulmonary Function test are normal? The normal range for any test is usually dependent on an individual’s gender, height, age, ethnicity and occasionally weight. Numerous studies have been performed on different population groups around the world in order to determine the their normal ranges.  One important finding has been that normal ranges differ not only between ethnicities but within them as well. The choice of a specific set of reference equations that best matches a given population has great implications on how the results are interpreted.  This is a problem that all Pulmonary Function Labs must face and is resolved with varying degrees of success.

The most commonly used reference equations for spirometry in the USA comes from the NHANESIII study.

[Click on graphs to expand]

[Click on graphs to expand]

[Click on graphs to expand]

[Click on graphs to expand]

[Click on graphs to expand]

[Click on graphs to expand]

[Click on graphs to expand]

[Click on graphs to expand]

The NHANESIII and other reference equations for spirometry, lung volumes (TLC, FRC, RV), Diffusing Capacity (DLCO) and the 6-minute Walk test are included in the Adult PFT Reference Equation spreadsheet:

Excel version

LibreOffice version

The Adult PFT Reference Equation spreadsheet is intended for educational purposes. Every attempt has been made to ensure the accuracy of the equations. Of note however, typographical errors and other inconsistencies were found in some of the publications the equations were taken from so complete accuracy cannot be guaranteed.  Please report any apparent errors so that they may be corrected.

In order to use the spreadsheet an individual’s height, age and weight are entered on the first tab of the spreadsheet. The results for different tests and genders are selected from the remaining spreadsheet tabs. 

For more technical and complete discussions of reference equations and normal values see:


Standing height, ethnicity and the vital capacity

What’s normal about FEV1 and how much does ethnicity matter?

What’s normal about the FEV1/FVC ratio?

The NHANESIII FEV1/FVC ratio and height, revisited

Evaluating spirometry predicted equations for the elderly

GLFI and the FVC, FEV1 and FEV1/FVC Ratio

COPD and the FEV1/FVC ratio. GOLD or LLN?


Is it time to scuttle the FEF25%-75%?

Lung Volumes:

What’s normal about RV and what does this have to do with TLC?

Diffusing Capacity:

What’s normal about DLCO?

6-minute Walk Test:

6-minute Walk Test

6MWT re-visited, now with the MCID!


Creative Commons License
PFT Patient by Richard Johnston is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

Leave a Reply

Your email address will not be published. Required fields are marked *