Physiological daily inhalation rates reported in our previous study for normal-weight subjects 2.6–96 years old were compared to inhalation data determined in free-living overweight/obese individuals (n = 661) aged 5–96 years. Inhalation rates were also calculated in normal-weight (n = 408), overweight (n = 225), and obese classes 1, 2, and 3 adults (n = 134) aged 20–96 years. These inhalation values were based on published indirect calorimetry measurements (n = 1,069) and disappearance rates of oral doses of water isotopes (i.e., 2H2O and H218O) monitored by gas isotope ratio mass spectrometry usually in urine samples for an aggregate period of over 16,000 days. Ventilatory equivalents for overweight/obese subjects at rest and during their aggregate daytime activities (28.99 ± 6.03 L to 34.82 ± 8.22 L of air inhaled/L of oxygen consumed; mean ± SD) were determined and used for calculations of inhalation rates. The interindividual variability factor calculated as the ratio of the highest 99th percentile to the lowest 1st percentile of daily inhalation rates is higher for absolute data expressed in m3/day (26.7) compared to those of data in m3/kg-day (12.2) and m3/m2-day (5.9). Higher absolute rates generally found in overweight/obese individuals compared to their normal-weight counterparts suggest higher intakes of air pollutants (in μg/day) for the former compared to the latter during identical exposure concentrations and conditions. Highest absolute mean (24.57 m3/day) and 99th percentile (55.55 m3/day) values were found in obese class 2 adults. They inhale on average 8.21 m3 more air per day than normal-weight adults.