How this calculator works
The four component volumes are tidal, inspiratory reserve, expiratory reserve and residual volume. Their sums define the standard lung capacities. Enter values measured under comparable conditions. Ordinary spirometry cannot directly measure residual volume, so a capacity that includes it requires an appropriate lung-volume measurement technique. The result is an estimate for information only and is not medical advice.
Formula
IC = IRV + VT. VC = IRV + VT + ERV. FRC = ERV + RV. TLC = VC + RV = IC + FRC. Inverse modes subtract the known component from the containing capacity.
Worked example
IRV 3000 mL, tidal volume 500 mL, ERV 1000 mL and RV 1200 mL give IC 3500 mL, VC 4500 mL, FRC 2200 mL and TLC 5700 mL.
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Frequently asked questions
Can a simple spirometer measure every input?
No. Residual volume remains after maximal expiration and requires methods such as gas dilution or body plethysmography.
Does a large total capacity prove healthy lungs?
No. Measured volumes need suitable reference values and clinical interpretation. These sums do not diagnose obstruction or restriction.
Why can a subtraction be rejected?
A component cannot be larger than the capacity containing it. Such an entry would produce a negative volume and is inconsistent with the definitions.