Wood as an organical material in the past was and in near future will stay one of the basic and most widely used construction materials. We can use different methods for clasification of sawn timber, for example dynamic methods and part of this method is to find out density of the wood, for instance using an instrument PILODYN 6J. This instrument presents a semi-destructive and faultless way to determine density of the wood in an inbuilt timber. The instrument determine depth penetrate a stud. Depth of the penetration by a stud is influenced mainly by density of the wood, but there are some other factors too and because wood is an anizotropic material we must taken into account: structure of the wood (springwood or summerwood), side of the board (external side or pith side), size of the angle between the penetrated stud and a tangent to annual rings and moisture of the wood. By experiment has been determining a significant dependence between densitiy of the wood and depth of the penetration by a stud and diference between depth of penetration on external and middle (pith) side of a board. The results proved a statistically significant dependencies. These detections will useful by measurement in laboratory conditions as well as in situ.