In design, it is common to use values for stress concentration factors (SCFs) obtained from textbooks. These textbook values have generally been obtained from photoelastic experiments for which Poisson's ratio will probably have a value greater than 0.3 and for frozen stress analysis a value approaching 0.5. However, when designing machine parts made from other isotropic materials, e.g. metals and structural ceramics, Poisson's ratio will probably have a lower value, which will affect the value of the SCF. In this paper, various stress-raising features have been analysed using the finite element method to determine the stress concentration factor. It is shown that Poisson's ratio can have a significant effect on the SCF.