Among the vital signs used to assess the overall condition of a patient, respiratory rate often changes earlier than heart rate and blood pressure before critical events such as thromboembolism and sepsis. Continuous respiratory rate monitoring is therefore important in both acute and chronic care settings. Small adhesive stretch sensors have emerged as a promising alternative to conventional monitoring technologies, because of their light weight and capability of localized measurements. However, the optimal anatomical placement site and orientation to maximize measurement accuracy have not been systematically investigated. In this study, we systematically evaluated the optimal placement strategy for adhesive one-axis stretch sensors (C-STRETCH^® MEASURE) by comparing six different sensor placement conditions at four anatomical locations (including chest midline and bilateral chest wall) in nine healthy male participants. Respiratory rate measured by an airflow sensor on a medical respiratory diagnostic device (PulSleep LS-140) was used as reference standard. Measurements were performed during four breathing protocols: spontaneous breathing and paced breathing at 10, 20, and 30 breaths per minute guided by metronome. Using the airflow sensor as reference, the respiratory rate error obtained from the stretch sensor under each condition and the extension rate served as evaluation metrics. Primary analysis was conducted using a linear mixed-effects model adjusted for inter-subject variability, breathing rate, and body mass index. The above-navel position produced extension rates of 8.0%-16.7%, compared with 2.9%-8.4% on the chest. Model analysis confirmed that the above-navel position yielded the lowest estimated marginal mean absolute error (0.600/min) among the six conditions in healthy men. The unadjusted Bland-Altman statistics served as supportive descriptions of agreement.