Respiratory Capacities: IC, EC, FRC, Vital Capacity and TLC
Biology · Breathing and Exchange of Gases · NEET
A "capacity" is just two or more lung volumes added together. The five NCERT capacities are: IC = TV + IRV, EC = TV + ERV, FRC = ERV + RV, VC = TV + IRV + ERV, and TLC = TV + IRV + ERV + RV. Memory hook: only TLC and FRC contain the Residual Volume (RV), because RV is trapped air you can never blow out; VC is everything you CAN move.
The four volumes (left) stack up; each capacity is a bracket grouping certain volumes. Note RV (red) appears only inside FRC and TLC, never in VC.
Your doubts, answered
What is the difference between a respiratory volume and a respiratory capacity?
A volume is a single, basic amount of air (TV, IRV, ERV, RV). A capacity is two or more of these volumes added together. So there are 4 volumes but 5 capacities. Whenever a question asks for IC, EC, FRC, VC or TLC, your job is just to add the correct volumes.
What is the formula for Inspiratory Capacity (IC)?
IC = TV + IRV. NCERT defines it as the total volume of air a person can inspire after a normal expiration. You start from a normal breath-out point, take a normal breath (TV) and then keep inhaling as much as possible (IRV).
Does Vital Capacity include Residual Volume?
No. VC = TV + IRV + ERV. Residual Volume (RV) is the air that always stays in the lungs and can never be breathed out, so it is never part of VC. Any option adding RV to VC is a trap. Only FRC and TLC include RV.
What is the difference between FRC and Vital Capacity?
They measure opposite things. FRC = ERV + RV is the air LEFT in the lungs after a normal breath-out (it contains RV). VC = TV + IRV + ERV is the maximum air you can MOVE in or out with force (no RV). So FRC is leftover air, VC is movable air.
How is Total Lung Capacity related to Vital Capacity?
TLC = VC + RV. In full form TLC = TV + IRV + ERV + RV. Since VC already equals TV + IRV + ERV, simply add the Residual Volume to VC to get TLC. TLC is the total air the lungs can hold after a forced inspiration.
⚠️ The NEET trap ✗ For EC when TV=500, ERV=1000 and RV=1200 are given, adding all three to get 2700 mL. ✓ EC = TV + ERV = 500 + 1000 = 1500 mL. Residual Volume is NOT part of Expiratory Capacity, so the 1200 mL is only a distractor. Only FRC and TLC use RV. 🧠 When RV is given in a capacity numerical, check if the capacity actually uses it before adding.
Real NEET questions
NEET 2019
Tidal Volume and Expiratory Reserve Volume of an athlete is 500 mL and 1000 mL, respectively. What will be his Expiratory Capacity if the Residual Volume is 1200 mL?
A · 1500 mL ✓
B · 1700 mL
C · 2200 mL
D · 2700 mL
Solution: Expiratory Capacity (EC) = Tidal Volume + Expiratory Reserve Volume = 500 + 1000 = 1500 mL. Residual Volume is not part of EC, so the 1200 mL value is only a distractor.
NEET 2019
The maximum volume of air a person can breathe in after a forced expiration is known as:
A · Expiratory Capacity
B · Vital Capacity ✓
C · Inspiratory Capacity
D · Total lung Capacity
Solution: This is the exact NCERT definition of Vital Capacity (VC = ERV + TV + IRV). It is the maximum air movable after a forced expiration. IC and EC are partial sums; TLC also includes residual volume.
NEET 2023 Phase 1
Vital capacity of lung is _______.
A · IRV + ERV
B · IRV + ERV + TV + RV
C · IRV + ERV + TV - RV
D · IRV + ERV + TV ✓
Solution: VC = IRV + ERV + TV. It does NOT include Residual Volume because RV can never be exhaled, so all options containing RV are wrong.
NEET 2024
Match List I with List II: A. Expiratory capacity B. Functional residual capacity C. Vital capacity D. Inspiratory capacity | I. ERV+TV+IRV II. TV+ERV III. TV+IRV IV. ERV+RV
There are five capacities: Inspiratory Capacity (IC), Expiratory Capacity (EC), Functional Residual Capacity (FRC), Vital Capacity (VC) and Total Lung Capacity (TLC). Each is a sum of two or more of the four respiratory volumes.
Which respiratory capacities include Residual Volume?
Only two: Functional Residual Capacity (FRC = ERV + RV) and Total Lung Capacity (TLC = TV + IRV + ERV + RV). IC, EC and VC never include RV.
What is Inspiratory Capacity (IC)?
IC = TV + IRV. It is the total volume of air a person can inspire after a normal expiration.
What is Expiratory Capacity (EC)?
EC = TV + ERV. It is the total volume of air a person can expire after a normal inspiration.
What is the formula for Total Lung Capacity?
TLC = TV + IRV + ERV + RV, which is the same as Vital Capacity + Residual Volume. It is the total air the lungs hold after a forced inspiration.
