This is a visual reference tying together all the lung volume and capacity terms — TLC, VC, RV, FRC, IC, ERV, IRV, and tidal volume — in one diagram, since the relationships between them are easy to mix up when learned as separate pages.
| Volume | Meaning | Typical |
|---|---|---|
| Tidal volume (Vt) | A normal quiet breath | ~0.5 L |
| IRV | Extra air you can inhale beyond a tidal breath | ~3.0 L |
| ERV | Extra air you can exhale below a tidal breath | ~1.2 L |
| RV | Air left after a maximal exhale | ~1.2 L |
| Capacity | Made of | Typical |
|---|---|---|
| IC | Vt + IRV | ~3.5 L |
| FRC | ERV + RV | ~2.4 L |
| VC | IRV + Vt + ERV | ~4.8 L |
| TLC | all four volumes | ~6.0 L |
Four non-overlapping volumes (left) combine into the overlapping capacities (brackets).
A volume is a single, non-overlapping compartment (IRV, tidal volume, ERV, RV). A capacity is two or more volumes added together (IC, FRC, VC, TLC).
IC = tidal volume + IRV. FRC = ERV + RV. VC = IRV + tidal volume + ERV. TLC = all four volumes (VC + RV).
Anything containing residual volume — RV, FRC, and TLC — because RV can't be exhaled. Those require body plethysmography, helium dilution, or nitrogen washout.
FRC is the lungs' resting volume between breaths; it keeps alveoli open and buffers oxygen, and it falls when lying flat or under anesthesia.