I'm currently working on a practical problem: How to measure your total lung capacity and/or your vital capacity accurately. Any suggestions or experience?
One of the methods that can be found with a quick google search is demonstrated in this video. You prepare a large water bottle by drawing a volume scale on its side. Then, you fill it with water, put it upside down into a sink and breathe into it via a tube. The air from your lungs will accumulate in the bottle and your scale will tell how many litres of water you replaced by air.
Another method is breathing into the microphone of your Smartphone... An app will evaluate the data. I am doubtful about the accuracy of this method. Any thoughts on this?
Finally, there are some more aspects to consider. Lung capacity is not the amount of air you breath out after a deep inhale. That quantity is called vital capacity. The above mentioned techniques are measuring vital capacity rather than total lung capacity. Since it is impossible to breath out all the air in your lungs, can you even measure total lung capacity without medical equipment? While measuring the vital capacity is a good starting point, I am ultimately interested in total lung capacity. The difference can be seen in this image from wiki - Lung volumes: