Use an inverted, water-filled bottle and a tube to capture the volume of exhaled air by water displacement. Counting marked volume intervals on the bottle estimates vital lung capacity.

1. Gather a large clear plastic bottle, a container or sink of water, a measuring jug, a waterproof marker, and a length of rubber or plastic tubing.
2. Use the jug to add 200 ml of water at a time to the empty bottle, marking a line at each 200 ml increment until you reach the top.
3. Fill the bottle completely with water, cap it, and submerge it upside down in a water-filled container so no air enters; remove the cap while the opening stays underwater.
4. Feed one end of the tubing up into the mouth of the inverted bottle while keeping the bottle opening underwater to prevent air leaks.
5. Take a deep breath, seal your lips around the free end of the tube, and exhale steadily into the bottle to push water out and trap your breath as an air space.
6. Count how many marked 200 ml intervals the water level drops; multiply the count by 200 ml to estimate your vital capacity.
7. Repeat 2–3 times with rest between trials and record the best consistent value.

Lung Capacity - a BodyWorks On Tour science experiment - Glasgow Science Centre:

📄 How to measure your lung capacity - BBC Bitesize: [https://www.bbc.co.uk/bitesize/articles/zm3xh39#zxyhhcw]]

• Use different increment sizes (eg 100 ml marks) for finer resolution in smaller lungs.
• Compare resting measurements with values after light exercise (ensure adequate rest before repeating).
• Normalize results by height or age and plot class data to look for trends.
• If available, compare bottle results with a handheld spirometer to check accuracy.

• Use individual, clean mouthpieces or disinfect the tubing between users to prevent cross-contamination.
• Do not perform the test if you have a respiratory infection or uncontrolled asthma; stop if you feel dizzy or short of breath.
• Avoid hyperventilating before the exhalation; breathe normally, then take one deep breath to start.
• Keep the bottle opening underwater during setup to prevent sudden water spills and to maintain a seal.
• Supervise handling of containers filled with water to prevent slips or spills; wipe up any water immediately.

• What is vital lung capacity? (The maximum volume of air you can exhale after a maximal inhalation.)
• Why do we multiply the number of lines by 200 ml? (Each line represents a calibrated 200 ml volume, so the count times 200 ml equals displaced air volume.)
• Why must the bottle be inverted and underwater? (To trap exhaled air in the bottle and force an equal volume of water out, enabling displacement measurement.)
• Which factors affect lung capacity? (Age, height, sex, and fitness level; training can increase capacity to a degree.)
• What happens in the chest when we exhale? (Intercostal muscles and diaphragm relax, chest volume decreases, pressure increases, and air is pushed out.)
• How could you improve measurement accuracy? (Use smaller increments, ensure a tight seal around the tube, read levels at eye height, and average multiple consistent trials.)