data = FileByteCount /@ FileNames["*.nb", FileNameJoin[{$InstallationDirectory, "Documentation", "English", "System", "ReferencePages", "Symbols"}]];
GraphicsGrid[ Partition[ Histogram[data, "Log", #, PlotRange -> All, PlotLabel -> #] & /@ {"Count", "LogCount", "Probability", "ProbabilityDensity"}, 2], ImageSize -> Large]