When designing a pipeline system, it is important to understand the pressure losses that will occur within the system. One common source of pressure loss is from elbow pipe fittings. There is extensive research available for pressure loss coefficients of elbow pipe fittings, but the research is derived from elbows with relatively smaller pipe diameters. The purpose of this research is to investigate pressure losses associated with larger diameter mitered elbows (36-inches to 144-inches). The dimensions for all mitered elbows considered in this research follow ANSI/AWWA C208-17 recommendations (AWWA 2017). Due to the large size of the mitered elbows of interest, physical testing was not feasible for this research. Therefore, this research used numerical methods to determine the pressure loss coefficients of large mitered elbows, reducing mitered elbows, and expanding mitered elbows. The results suggest a strong correlation that the pressure loss for large mitered elbows, presented in this research, are solely dependent on the pipe Reynolds number. The reducing and expanding mitered elbows showed the pressure loss coefficient is dependent on Reynolds number and the percent of reduction/expansion of the elbow. Tabulated data, graphical data, and recommended equations are presented to determine pressure loss for large mitered elbows, reducing mitered elbows, and expanding elbows.