Soil structure exerts important influences on the soil conditions and this is often expressed as the morphometric measure of its porosity. The measurement systems used until now to evaluate the size, shape, quantity and continuity of the soil pores in two dimensional images at the field scale seem a little outdated. However, the use of image analysis for the purpose has been controversial and it is necessary to improve and standardise some important details of image analysis procedures. Aiming for the separation between round, elongated and irregular pores, it was necessary to create a system of evaluations that would complement the habitually used ‘shape factor’. It was also necessary to include the measurement of other variables, like the diameter, length and width of the complex and irregular cracks that in most cases are impossible to evaluate only with the variables obtained directly from the image analyzers. So, it was necessary to develop and test algebraic equations that would lead to those evaluations. This paper presents a morphometric system that leads to a model of typological classification of soil macroporosity at a field scale. So, this paper contributes toward the normalization of the image analysis techniques, which allows studies to be more rigorous, accurate and quicker, with an acceptable ratio of errors.