Different types of solid bodies (particles) with specific shape and size are needed for industrial processes. For spherical particles, 'sizer' measurements are usually reported as sphere diameters. For non-spherical particles, particle shape and especially orientation must be taken into account. Particles of a specific shape will present different views when looked at from different directions. We have employed a Camsizer(R) instrument to measure the distribution of projected area under different physical conditions for solid cylindrical particles: . Under 'ideal' conditions, corresponding to a uniform distribution of particle orientation, measurements agreed with predictions. The celebrated theorem of Cauchy applies only to this case. . For two other situations, measured and predicted results differed. However, from the experimental data it was possible to infer the particle orientations and hence theoretically predict the projected area distribution. Excellent agreement between theory and practice was then restored. (C) 2004 Elsevier Ltd. All rights reserved.