Size of Warhammer figures? Not scale, SIZE

Okay I've been thinking about painting a couple warhammer 40k figures since those space marines are oh-so-cool.  Anyways, I've heard they are 28mm or roughly 1/60 scale.  But heres the question.  For example, the 28mm refers to how tall a standard 5'11-6' or so man would be in that scale.  So A figure of an imperial guard or something would be just that, around 28mm.  But a steroid filled, genetically modifed beast of a man in extremely big power armor (A space marine) Would proabably be a good amount bigger.  Not to mention that figures are always bigger than said.  For example 54mm models always seem to measure in the 60mm range.  So how tall is a space marine in terms of mm?  How would it look next to a 1/35 figure?  I know it would be smaller but I build 1/35 so that would be the best reference to me.  Thanks!