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Pneumothorax Percentage Calculator

Check Illustration Below

Representation of Collins Method of Calculating Pneumothax Volume Percentage based on interplueral distances.

Formula for calculating Pneumothorax Volume based on Collins Method using Interpleural Distances:

Pneumothorax Volume Percentage = 4.2 + [4.7 x A+ B + C]

A + B + C = Sum of Interpleural Distances.

4.2 = Correction Factor.

Sum of Interpleural Distance (cm)Percentage volume of Pneumothorax
Estimation of Pneumothorax Volume on Chest Radiographs Based on the Collins Method

What are the different methods to estimate pneumothorax on chest radiographs?

Light Index:

To calculate the light index, 2 measurements are required,
DL – Diameter of the collapsed lung
DH – Diameter of the hemithorax on the collapsed side
Light index is given : % of pneumothorax = 100−(DL3/DH3×100)

Rhea Method:

Average interpleural distances (AID) measured in centimeters at the apex, midpoint of the upper half of the lung, and midpoint of the lower half of the lung on an erect chest X-ray to estimate pneumothorax size in percent by using a nomogram.

Collins Method :

Collins method is based on the formula mentioned above.

Here is an excerpt from the methods section of that study:

“All patients underwent an erect inspiratory posteroanterior radiograph and a helical CT scan of the thorax on the same visit to the radiology department. The interpleural distance was measured at three locations, and the figures were added together. Following helical CT of the thorax, the percentage pneumothorax size was calculated by drawing regions of interest around the relevant hemithorax and lung on 10-mm reconstructed
slices. A scattergram of the sum of interpleural distances in centimeters versus percentage pneumothorax size was plotted”

American Thoracic Society (ATS) Guidelines:

Distance from the apex of the chest to the lung cupola in cm.

British Thoracic Society (BTS)

Distance between the lung margin and the chest wall at the level of the hilum

Which is the most accurate method for estimating Pneumothorax volume on a chest radiograph?

Collins Method is the most accurate among the presently available methods.

When is intervention suggested for a pneumothorax?

Conservative management is suggested for small pneumothoraces, while larger pneumothoraces need intervention.

Definitions of small pneumothorax include:

  • BTS Method: <2 cm between the lung margin and the chest wall at the level of the hilum
  • ATS Method: <3 cm from apex to cupola (ATS)
  • Light’s, Rhea and Collins Method: <25%


  1. Quantification of pneumothorax size on chest radiographs using interpleural distances: regression analysis based on volume measurements from helical CT. C D Collins, A Lopez, A Mathie, V Wood, J E Jackson, and M E Roddie American Journal of Roentgenology 1995 165:5, 1127-1130
  2. Devaraj, U., Ramachandran, P., Krishnaswamy, U. et al. Comparison of methods to quantitate spontaneous pneumothorax — A study from a tertiary care hospital. Egypt J Bronchol 13, 388–393 (2019).

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Disclaimer: The author makes no claims of the accuracy of the information contained herein; this information is for educational purposes only and is not a substitute for clinical judgment.

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About the Author

Dr. Amar Udare, MD, DNB

Dr Amar Udare Dr. Amar Udare is a board-certified radiologist. He is a clinical assistant professor at the University of Calgary. He has a passion for teaching (#FOAMrad and #FOAMed) and has been a semi-finalist for the 2018 and 2020 Aunt-Minnie Most effective Radiology Educator Awards. He has authored multiple peer-reviewed publications which can be accessed on PubMed and Google Scholar.


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