Silane-nitrous oxide mixtures, widely used in the semi-conductor industry, are very hazardous. Since the silane readily decomposes into silylene and hydrogen molecules, a good knowledge of H2-N2O kinetics is required to evaluate the risks of utilization. Although numerous ignition delay time studies on H2-N2O mixtures exist, there is a limited number of detonation cell size data. The purpose of the present study is to provide additional experimental data and to estimate several methods to predict the cell size. Detonation cell size was measured in mixtures diluted with 20, 40 and 60 mol% argon at initial pressures and equivalence ratios ranging between 7 and 35 kPa and between 0.3 and 2.5, respectively. It is shown that at initial pressure as low as 35 kPa, H2-N2O-Ar mixtures become very sensitive to detonation with cell size of few millimeters. Using a detailed chemical kinetic model, the semi-empirical correlation from Ng has been proven to give accurate prediction of cell size. After a specific reduction of the detailed scheme and the adjustment of the detonation velocity to match the experimental one, a 2-D Euler code has been shown a capability to provide reliable cell size data for stoichiometric mixtures.