Based on the recent research by Ghajar et al., special attention should be given to the pressure sensing diaphragms for the measurements of friction factor in micro-tubes. In their research, they focused on how the micro-tube diameters influenced the transition region. This study complements their study. Using their suggested diaphragm selection method, micro-tubes with diameters around 1000 μm and five different surface roughness values ranging from 0 to 4.3 μm were used to study the friction factor characteristics across the laminar, transition and turbulent regions (800<;Re<;7000). Moreover, the influence of surface roughness on the start and end of the transition region was observed. It was concluded that a narrower transition region can be seen with an increase in the surface roughness