During drilling and cementing operations, many stand-off devices, such as centralizers, stabilizers, reamers, turbulators, cutting bed impellers, and friction reduction devices are widely used. Some of these devices are designed to enhance the displacement efficiency during cementing operations, to increase hole cleaning efficiency, or to reduce torque and drag during drilling operations. The hydraulics program for the deep and especially ultra deep wells constitutes a significant portion of the well planning. Challenges associated with extreme depth and different types of downhole tools used in the drillstring translate to additional problems to the well design. Few studies have explored the pressure losses arising from these attached devices in the drillstring or casing string, and the pressure losses caused by them are assumed either negligible or ignored. The geometrical designs of these devices are relatively irregular and complicated, which is one of the major difficulties for pressure loss calculations. Non-Newtonian drilling fluids further complicate the problem. A study is necessary to determine the impacts of these devices on the pressure loss calculations and thereby the effects on downhole circulating density. These devices alter the flow stream and especially the angular bladed type cause the flow to swirl. This flow is complex, which underpins the effects of the pressure drop calculation across these devices. The paper describes a method and equations to calculate the pressure losses due to the stand-off devices.