The correct computer simulation of the powder compaction stage requires the determination of the elastoplastic parameters which characterize its mechanical behavour. Instrumented dies are frequently used to monitor the longitudinal and radial stress occurring during powder compaction. When strain gages are employed a previous calibration is needed. Many sources of error exist that can lead to the incorrect calibration of the instrumented die. By means of a FEM simulation some of these problems are analysed. The effect of die wall thickness, compression length, and strain location are studied.