The paper focuses upon one aspect of the use of image analysis technique to characterise the size of particles to high accuracy for certified reference material purposes. An object of the simulation was to investigate the parameters required to achieve measurement errors of less than 1%. The calibration of indirect particle sizing techniques such as laser diffraction, dynamic light scattering etc. Require certified reference materials, preferably having a high accuracy both in size and quantity. To improve the accuracy of reference materials Witt et al. [1] proposed a picket fence of nearly mono-sized, solid, uniform density spherical particles, where precise weights of each mono-sized fraction were to be added together to form a defined distribution. For this method to succeed high particle size accuracy, coupled with precision weighing and particle handling techniques are vital. A pixel array has been modelled to examine the influence, upon image analysis measurement accuracy, of pixel number, threshold levels and image centring.