The design and preparation of isotropic silver nanowire-polystyrene composites is described, in which the nanowires have finite L/D (< 35) and narrow L/D distribution. These model composites allow the L/D dependence of the electrical percolation threshold, ϕc, to be isolated for finite-L/D particles. Experimental ϕc values decrease with increasing L/D, as predicted qualitatively by analytical percolation models. However, quantitative agreement between experimental data and both soft-core and core–shell analytical models is not achieved, because both models are strictly accurate only in the infinite-L/D limit. To address this analytical limitation, a soft-core simulation method to calculate ϕc and network conductivity for cylinders with finite L/D are developed. Our simulated ϕc results agree strongly with our experimental data, suggesting i) that the infinite-aspect-ratio assumption cannot safely be made for experimental networks of particles with L/D < 35 and ii) in predicting ϕc, the soft-core model makes a less significant assumption than the infinite-L/D models do. The demonstrated capability of the simulations to predict ϕc in the finite-L/D regime will allow researchers to optimize the electrical properties of polymer nanocomposites of finite-L/D particles.