Lung Capacity Calculator

How to use this lung capacity calculator

What this calculator does

This calculator converts four static lung-volume measurements into four standard lung capacities. It calculates total lung capacity (TLC), vital capacity (VC), functional residual capacity (FRC), and inspiratory capacity (IC) using direct addition identities. The tool is useful for checking arithmetic from a pulmonary-function report, teaching how lung volumes combine, or exploring how a change in one component affects several capacities. It does not estimate a predicted normal value from age, sex, height, or ancestry, and it does not interpret whether a measured result is clinically normal or abnormal. The NHLBI overview of pulmonary function testing describes TLC, FRC, VC, and IC as standard lung-volume measurements used in respiratory testing.

When to use it

Use it when you have measured IRV, TV, ERV, and RV values and want a consistent capacity calculation; when studying respiratory physiology and checking the relationships among volumes; when converting a set of measurements between liters and milliliters; or when preparing a neutral worksheet for discussion with a clinician or instructor. Because residual volume is not obtained by ordinary simple spirometry alone, make sure the RV value comes from an appropriate lung-volume measurement method when you are using real clinical data.

How to calculate

1. The calculator opens with a complete demonstration set: IRV 3.0 L, TV 0.5 L, ERV 1.1 L, and RV 1.2 L. The results and a validated example Excel workbook are available immediately.
2. Replace each demonstration value with your measured lung volume. Enter plain decimal numbers using a period as the decimal separator. Comma thousands grouping is accepted when unambiguous; decimal-comma input and scientific notation are rejected to avoid silent reinterpretation.
3. Use Display unit to switch between liters and milliliters. The calculator converts the current values, recalculates every capacity, updates the composition chart and tables, and exports the workbook in the active unit.
4. Read TLC as the complete sum, then use VC, FRC, and IC to see the standard combinations relevant to maximal exhalation, relaxed end-expiration, and inspiration from a normal end-expiratory level.
5. Select Download Excel to export the current validated state as a real .xlsx workbook. Reset clears the demonstration and all calculated content; after Reset, Excel export stays disabled until all four required measurements are complete and valid again.

Input guide

Inspiratory reserve volume (IRV) is required and accepts a finite nonnegative volume in the selected unit; 3.0 L is the demonstration value. Increasing IRV raises TLC, VC, and IC by the same amount, but does not change FRC. Do not confuse IRV with inspiratory capacity, which also includes tidal volume. Tidal volume (TV) is required; 0.5 L is the example. It represents the air moved in a normal breath, so increasing TV raises TLC, VC, and IC while leaving FRC unchanged. Expiratory reserve volume (ERV) is required; 1.1 L is the example. A higher ERV raises TLC, VC, and FRC, but not IC. Residual volume (RV) is required; 1.2 L is the example. It is the air remaining after maximal expiration, so increasing RV raises TLC and FRC but does not change VC or IC. For all four fields, blank text, negative values, unsupported symbols, decimal-comma forms such as 1,5, and scientific notation such as 1e3 are rejected. A value of zero is mathematically accepted, although a zero measured physiologic component may be implausible and should be checked at the source.

Display unit is a required control with two options: Liters (L) and Milliliters (mL). Switching the unit converts the current measurements rather than merely relabeling them. For example, 0.5 L becomes 500 mL. The canonical calculation remains the same physical quantity, so a round trip from L to mL and back returns the original values apart from harmless display formatting.

Output guide

Total lung capacity (TLC) is the primary result and equals IRV + TV + ERV + RV. Vital capacity (VC) equals IRV + TV + ERV and excludes residual volume. Functional residual capacity (FRC) equals ERV + RV and describes the volume remaining at the end of a normal passive expiration. Inspiratory capacity (IC) equals IRV + TV. All four results use the selected volume unit and are exact arithmetic identities before display rounding. The header pills repeat the same canonical TLC, VC, FRC, and IC values for quick scanning. The Volume breakdown table lists each measured component, its entered value, and its percentage share of TLC. The composition chart uses the same four component values; each colored segment is a share of the same TLC total, not a separate predicted range. The Capacity calculation details table lists each capacity, its formula, and its current result.

Worked example

With the startup example, IRV = 3.0 L, TV = 0.5 L, ERV = 1.1 L, and RV = 1.2 L. TLC is 3.0 + 0.5 + 1.1 + 1.2 = 5.8 L. VC is 3.0 + 0.5 + 1.1 = 4.6 L. FRC is 1.1 + 1.2 = 2.3 L, and IC is 3.0 + 0.5 = 3.5 L. The composition chart therefore represents IRV as about 51.72% of TLC, TV as 8.62%, ERV as 18.97%, and RV as 20.69%. These exact startup values are also the first workbook checkpoints in the downloadable example.

Learn more

For clinical context, MedlinePlus explains lung function tests and body plethysmography, including why lung-volume testing is used to measure the amount of air the lungs can hold and the air remaining after maximal exhalation. For measurement methodology and quality standards, the PubMed record for the 2023 ERS/ATS lung-volume technical standard summarizes the specialist standard for measuring and reporting static lung volumes.