To investigate statistics of the clusters of coherent fine scale eddies, direct numerical simulation databases of homogeneous isotropic turbulence up to Re_λ =344.1 have been analyzed. To measure the length scale of the clusters quantitatively, PDF variance, which is based on deviations of the concentration PDF (probability density function) of the coherent fine scale eddy from that of an uniform field, has been introduced. The concentration measure reveals that the mean distance of the coherent fine scale eddies is Taylor micro scale and the size of the cluster of the strong coherent fine scale eddies is about the integral length scale.