Rock blocks due to different joint types are classified qualitatively into three categories as bars, plates and prisms. In engineering evaluations, their quantitative descriptions based on the field observations leading to reliable design values are of prime importance. Simple conceptual models of rock fragments coupled with scanline measurements provided objective relations between the rock quality designation (RQD), volumetric, areal or linear (along scanline) joint counts (J(upsilon)) and block volumes (V). The main purpose of this paper is to derive relevant relations for logarithmically-distributed intact lengths. Due to the complexity of these relations, the results are presented in the form of various charts which it is hoped provide useful tools for any rock engineer. The charts presented are for standard deviations equal to unity; however, charts for any desired value of standard deviation can be prepared from the relevant equations. The implementation of the methodology is performed for actual field data. A significant conclusion is that the negative exponential distribution provides a single volumetric RQD-value (which is different from the directional RQDs) and the log-normal distribution gives almost the same result within practical limits, both for directional and volumetric RQD values.