The aim of the study was to verify the commonly used conversion factors, their realignment and adaptation to current requirements for wood group S2. Our re-evaluation was based on medium-sized pine and spruce wood between 1 m and 3 m long, with an upper diameter of 5 cm to 24 cm without bark. Measurements were carried out on individual raw material pieces (rollers) as well as entire stacks. In total, 1092.026 steres of pine wood and 482.430 steres of spruce wood from five different forest districts were measured. The conversion factors for both pine and spruce were observed to be generally lower than those currently used in PN-D-95000-2002 and the directives of the General Director of State Forests regarding technical requirements on medium-sized round wood. We also confirmed the dependence between the value of the conversion factor and the average diameter of the roller in the stack, although this was not consistently statistically significant due to the influence of a multitude of factors that potentially cancel each other out. The differences of conversion factors obtained for the S2A and S2B groups suggest that more extensive research for pine and spruce wood as well as the development of separate conversion factors is necessary. However, developing appropriate conversion factors for wood of the S2A group (S2AC and S2AP), especially pine wood, will be challenging due to the large range of diameters and curvature permitted by the regulations
