Our aim was to study the effect of dietary physical characteristics on size of washed faecal particles from finishing pigs (98±6 kg). The pigs were fed either a finely ground pelleted diet (FP) or a coarsely ground meal diet (CM) comparable in all ingredients. The diets were based on barley, wheat and soybean meal as the main ingredients and were either ground through a 2 mm screen before pelleting or ground to pass a 4.5 mm screen. Faecal samples were collected from 7 FP and 8 CM fed pigs and washed in nylon bags before drying and sieving into 3 fractions: >1 mm, 0.5-1 mm and bottom bowl. Samples of particles from the sieving fractions were scanned and the length and width of individual particles were identified using image analysis software. The overall mean, mode and median were estimated from a composite function. The dietary physical characteristics significantly affected the proportion of faecal particles retained in the bottom bowl and >lmm sieving fractions (P = 0.001). Particle dimensions in each sieving fraction (P = 0.05) were altered as well as the overall means (P = 0.01) 2.7±0.2 vs. 0.77±0.03 (length) and 1.45±0.22 vs. 0.47±0.04 (width) for CM and FP treatment, respectively.