An accurate, physically based mathematical model for characterisation of inkjet printers would allow the minimum set of observations to be used to derive wellconditioned workable printer characterisations with known error characteristics.This paper seeks to present such a method of directly computing the characterisation of an inkjet printer from a limited set of colorimeter measurements. The method (called the Double Neugebauer Model by the author) employs a variation of the Neugebauer ink-mixing model and uses least squares to fit the model to the measured data. The method has been verified for a limited range of inkjet printers and shown to have an accuracy to the order of RMS ΔE = 1 on those printers. The resulting characterisation can be inverted numerically and used to produce a printer characterisation profile when combined with gamut mapping techniques.