During mask ventilation, the mask volume can vary as it is pressurized or when it is squeezed. The change in volume of the mask may affect tidal volumes delivered and difference in inspired (Vti) and expired tidal volumes (Vte). Objectives: To investigate whether hand squeeze and distensibility of the mask during ventilation influences tidal volume measurements. Methods: For both experiments, we ventilated a leak-free mask ventilation model using pressures of 25/5 cm H2O through a t-piece. Vti and Vte were measured. (A) Two consultants performed mask ventilation with (1) consistent hand squeeze, (2) release during inflation and squeeze during expiration, (3) squeeze during inflation, release during expiration, and (4) gentle squeeze. Results: (B) Thirty caregivers performed mask ventilation. Experiment A: Vti was different during consistent hold (1) 8.1 ml (0.4) and loose grip (4) 8.2 ml (0.3), compared to squeezing during inflation (2) 18.9 ml (1.9), or expiration (3) 6.4 ml (3.5). Variance in difference between Vti and Vte occurred only when the mask was squeezed during inflation (-47.4 (101.5)). Experiment B: volumes measured were consistent (intraindividual CV 3-5 , interindividual CV 9-10 ). When comparing gas flow rate of 6-10 l/min, volumes increased by approximately 8 , differences in Vti and Vte were small with both flow settings (-0.9 (-3.9-1.4) and -0.6 (-3.3-1.8); n.s.). Conclusion: Variation in mask hold during mask ventilation can influence volume measurement, but this hardly occurs when testing caregivers.