Pinch the balloon closed. Have a partner fit the string around the balloon at the widest part. Measure the length of the string in centimeters, around the circumference of the balloon and record the measurement. Repeat steps 2-4 four more times. Calculate the average circumference of the five measurements.
Tidal volume is the amount of air expelled during a normal breath.
Calculate the average tidal volume using the average balloon radius. Multiply the average tidal volume by the average number of breaths per minute to calculate the amount of air you inhale per minute. Divide the number of milliliters of air by 1000 to get the number of liters of air you inhale per minute.