This paper deals with the experimental strain, stress and deflection analysis of a cubic box subjected to concentrated loads applied at the centre of two opposite faces. The ratio between the inside span and the wall thickness varied between approximately 5 and 14. All corners had circular fillets. The experimental analysis was conducted using mechanical and electrical strain gauges and brittle coatings. Results, given parametrically by means of a family of curves representing normalized stresses, are applicable to boxes of any size, made of any elastic materials, provided the wall thickness falls within the investigated range. Some results obtained using the theory of structures approach are included for comparison purposes and presented in a form useful to designers.