Main objective of this work is design, assembly and characterization of measuring line for flow measurement of air with orifice plate that has nominal diameter DN25. After selecting required components and assembling the measuring line, multiple measurements were performed. The flow and the measurement uncertainty for each point were calculated. There were two ways to establish the air flow, by small cooling fan and hairdryer. A theoretical part of the task was made first, where the history of flow measurement, flow metering and terminology related to flow measurements were done. After that, measurement line was constructed to fit the orifice plate that we were using, with the computer simulation and aplication of the theory we bought the tube and fan we needed. The line was assembled in the Laboratory for Process Measurements, and measurements were also made there. Measurements were made to select the nominal pressure drops, seven for the fan and six for the hair dryer, and the goal was to calculate the flow for each point. Flow calculation was made according to the characterization of the metering line that was made after assembly and before measurement according to ISO 5167. After measurement and flow calculation, measurement uncertainty as well as analysis of results were determined. All measurements were made in the Laboratory for Process Measurement at the Faculty of Mechanical Engineering and Naval Architecture, and most of the equipment used for setting the measurement line was from the LPM, except the fans and pipes that were purchased for construction of measurement line.