Test results from cores with diameters smaller than the standard sizes and with length-to-diameter (Vd) ratios less than I are considered to be unreliable due to higher variability in concrete strength. There is, however, still a lack of evidence in the literature regarding the unreliability of the compressive strength data for these lower-volume cores. Significantly important is the missing verification of such statements concerning the random variations of concrete strength, supported with statistical approaches. Statistically significant data sets under such conditions are very rare. In this study, the issue was addressed by exploring the features of the compressive strength obtained from different diameter cores using probabilistic concepts in particular, when the Vd is less than l and shed light on the uncertainty regarding the reliability of the data taken under these conditions. The major outcome of this study is that concrete cores with diameters less than the standard-size cores and larger than microcores could be effectively used in practice to represent the variations in concrete strength, provided that the number of core samples and lid are sufficiently high.