Occupant merging behavior on stairwell landings is analyzed through the study of evacuation videos. Both flow rate and transit time analyses are conducted. Data is compared to the hydraulic model, which is presented in Chapter 3 of the SFPE Handbook. It is found that the flow ratio, which is the actual outflow rate from a merging event divided by the expected outflow per the hydraulic model, is on average 75%. The transit ratio, which is the normal transit time of the stairwell landing divided by the merging transit time, is found to be 0.67 and 0.70 for the floor and stair flows, respectively. Empirical data is compared to data collected from the Pathfinder 2011 egress model. Causes and influencing factors of occupant merging are proposed.