Vegetable grain materials are an important group of agricultural materials and agricultural raw materials. Due to their specific structure and difficulties accompanying both studies and description of this structure, a lot of their properties have not been recognized yet. At present, little is known about phenomena that take place in a contact spot between individual components of a grainy mass. A significant factor influencing the behavior of the whole arrangement is the seed contact surface changing in relation to the moisture level and load. The authors presented their own study on a method for the defining of the contact surface between a pair of grains. The method described makes it possible to take measurements at various levels of water content in the material and at various levels of compression forces. The idea of the measurement is based on the geometrical analysis of the consecutive cross-sections of the pair of grains studied. A plane comprising a contour of the contact surface is perpendicular to the surfaces of the cross-sections. In every cross-section, measurements of the length of the contact line and distance between the contact line and the base line were taken. The measurements allow for the calculation of the contact surface area and determination of its shape, as well as for the drawing of the contact surface.