A method for the systematic selection of paediatric CT technique factors is described. The approach is based on the assumption that the level of image noise acceptable for a given adult CT image is also acceptable for the equivalent paediatric examination. A simple exponential attenuation model is proposed. Effective linear attenuation coefficients were initially established from a series of phantom measurements simulating head, chest and abdomen examinations at 120 kVp, then extended for a range of tube potentials and beam qualities using a beam spectral model. Application of the method is demonstrated using phantoms representing head, chest and abdomen sections for neonate and ages 1 year, 5 years, 10 years, 15 years and adult.