The division of soils into granulometric groups according to the PTG 1956, used on soil-agricultural maps, is incompatible with the USDA classification, the most widespread worldwide, and the new PTG 2008 division based on it. The aim of this study was to propose attribution of the content of soil separates according to the USDA classification to chosen soil species – granulometric groups – according to PTG 1956 division, shown on soil-agricultural maps of Poland. Soil-agricultural maps updated in this way can be used to model the impact of climate change on the environment and agriculture, erosion, and hydrological phenomena within the area of Poland. A dataset of 1085 soil samples from 15 localities and seven provinces of Poland was used to achieve this goal. These samples were classified into 18 granulometric groups according to PTG 1956, and 11 soil texture classes according to the USDA classification – all except silt. For the available dataset of soil samples, the mean and median contents of sand, silt, and clay were calculated for each soil species, according to both the PTG 1956 and PTG 2008/USDA classifications. Universal, simple, and multiple linear regression equations were also developed for estimating soil separates contents according to the PTG 2008/USDA classification, based on known contents of these separates in granulometric groups according to the PTG 1956 classification. The main soil texture class according to PTG 2008/USDA, which can be attributed to each soil species according to the PTG 1956, was determined, which made it possible to relate the results of our research to those of other authors, which also concerned the comparison of soil texture according to the two classifications mentioned above. Based on our research and that of other authors, a preliminary proposal is presented for attributing the content of sand, silt, and clay separates according to PTG 2008/USDA classification to PTG 1956 granulometric groups. It is recommended to verify and improve the presented proposal using, for example, the grain size curve. The universality of the use of the developed methodology could be improved by extending the database of soil samples, particularly with the less represented granulometric groups according to the PTG 1956 classification, such as silty loose sand (plp), silty weakly loamy sand (psp), silty light loamy sand (pglp), clay (i), ordinary silt (płz), and clayey silt (płi). There is also a need for a separate study on specific soil species such as colluviums, alluviums, loesses, rendzinas, mountain soil, and gravels, which are shown on soil-agricultural maps covering more than 10% of Poland’s agricultural land. The attribution of sand, silt, and clay separates according to PTG 2008/USDA classification depending on the geological origin of particular soil parent materials, particularly in the case of silts and clays according to PTG 1956, should be considered.