Objective measurement of resting metabolic rate (RMR) may be important for optimal nutritional care but is hindered by the price and practicality of the metabolic monitoring device. This study compared two metabolic monitoring devices for measuring RMR and oxygen consumption (VO2) and compared the measured RMR with the predicted RMR calculated from equations. RMR was measured using QUARK RMR (reference device) and Fitmate GS (COSMED) in a random order for 30 minutes, each on fasted participants. In total, 68 adults participated (median age 22 years, interquartile range 21-32). Pearson correlation showed that RMR (r=0.86) and VO2 (r=0.86) were highly correlated between the two devices (p<0.05). Intraclass Correlation Coefficients (ICC) showed good relative agreements regarding RMR (ICC=0.84) and VO2 (ICC=0.84) (p<0.05). RMR measured by QUARK RMR was significantly higher (155±180 kcal/day) than Fitmate GS. Equations significantly overpredicted RMR. Accurate RMR (i.e. within ±10% of the RMR measured by QUAR RMR) was found among 38% of the participants for Fitmate GS, and among 46-68% depending on the equations. Bland-Altman analysis showed a low absolute agreement with QUARK RMR at an individual level for both Fitmate GS (limits of agreement (LOA):-198 to +508 kcal/day) and equations (LOA ranged from-473 to +449 kcal/day). In conclusion, both Fitmate GS and predictive equations had low absolute agreements with QUARK RMR at an individual level. Therefore, these limitations should be considered when determining RMR using Fitmate GS or equations.