Background: Emergency Department Length of Stay (ED-LOS) is a crucial measurement for clinical and operational decisions and is used for regulatory reporting and research purposes. Accurate and standardized measurement of this duration improves the effectiveness of decisions and findings. Further, automated capture can eliminate dependence on human task-based data-entry. Objective: Compare a real-time location system (RTLS)based measure of LOS against the current standard of practice (EMR); examine factors associated with discrepancy in LOS. Method: Estimation of LOS using the first and last RFID record in the RTL system, and statistical assessment of their similarity to the corresponding measurement from the EMR. Result: Length of stay durations from the two methods have very similar distributions, with a slight shift. Conclusion: RTLS provides an efficient and standardized means to measure LOS.