Inertial measurement unit is a device that can measure orientation and the state of motion. Usually, these measurements combine the readings from accelerometer, gyroscope and magnetometer. Before the actual orientation can be calculated, the device needs the ask the information from the sensors, synchronize it with the data from other sensors and nally calibrate the sensor reading. The goal for this thesis is to describe the development process to produce a small-sized wirelessly controlled inertial measurement unit which is designed to work in wearable environments. The thesis is divided in three parts. The rst section describes the reasons for selecting the components, the printed circuit board design and mechanical design. The second part focuses on the software running on the device and describes the software architecture and the inner workings individual software components. The last part introduces a method which is used to calibrate the accelerometer and gyroscope readings. The results of this method are also presented. This section also describes how the measurement unit is used in real-life measurement situations. Based on these measurements, it can be said that the performance of the inertial measurement unit is at su cient level.