Functional Residual Capacity Calculator

Estimates FRC based on expiratory reserve and residual volume.

In the text below the form there is more information about the variables and the formula used.

The functional residual capacity calculator uses the expiratory reserve and residual volume, obtained during a ventilator pulmonary function test, to determine the FRC value.

Functional Residual Capacity = Expiratory Reserve Volume + Residual Volume

In short form:


The average value for FRC is around 2.4 L for men and 1.8 L for women.

Expiratory reserve volume
Residual volume
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Steps on how to print your input & results:

1. Fill in the calculator/tool with your values and/or your answer choices and press Calculate.

2. Then you can click on the Print button to open a PDF in a separate window with the inputs and results. You can further save the PDF or print it.

Please note that once you have closed the PDF you need to click on the Calculate button before you try opening it again, otherwise the input and/or results may not appear in the pdf.


Variables and formula

The functional residual capacity is one of the four lung capacities determined through respiratory tests. The other parameters are: the vital capacity, inspiratory capacity and total lung capacity.

FRC is defined as the volume of air that remains in the lungs at the end of passive expiration (after a normal expiration).

There are two pulmonary volumes, measured via spirometer (ERV) or estimated (RV), required to calculate FRC:

Respiratory volume Description Normal values
Expiratory reserve volume Represents the volume of air that can be exhaled during a forced expiration and after the normal expiration. 1.2 L for men
0.7 L for women
Residual volume Represents the volume of air that remains in the lungs after a forced expiration and is more complex to determine, being measured indirectly. 1.2 L for men
1.1 L for women

The formula used by the above calculator is:

Functional Residual Capacity = Expiratory Reserve Volume + Residual Volume

In short: FRC = ERV + RV


About functional residual capacity

The average value for FRC is around 2.4 L for men and 1.8 L for women. There are also tables with predicted values dependent on patient age, gender and height.

Abnormal FRC values are in most cases indicative of a respiratory condition and should prompt further investigations.

Increases in FRC are met in emphysema whilst decreases in FRC are usually met in obese patients due to the thoracic pressure of the fat tissue.

As a result of increased FRC, total lung capacity also increases.

Residual volume, the estimated component of the FRC, can be measured through:

■ Pulmonary plethysmography;

■ Radiographic planimetry;

■ Closed circuit helium dilution;

■ Nitrogen washout.



1. Gommers D. Functional residual capacity and absolute lung volume. Curr Opin Crit Care. 2014; 20(3):347-51.

2. Quanjer PH, Tammeling GJ, Cotes JE, Pedersen OF, Peslin R, Yernault JC. Lung volumes and forced ventilatory flows. Report Working Party Standardization of Lung Function Tests, European Community for Steel and Coal. Official Statement of the European Respiratory Society. Eur Respir J Suppl. 1993; 16:5-40.

3. Crapo RO, Morris AH, Gardner RM. Reference Spirometric Values using Techniques and Equipment that meet ATS recommendations. American Review of Respiratory Disease. 1981; Volume 123, pp.659-664.

Specialty: Pulmonology

System: Respiratory

Objective: Determination

Type: Calculator

No. Of Variables: 2

Abbreviation: FRC

Article By: Denise Nedea

Published On: June 8, 2017

Last Checked: June 8, 2017

Next Review: June 8, 2023