An Etymological Dictionary of the German Language/Annotated/Spanne
Spanne, feminine, ‘span,’ from Middle High German spanne, Old High German spanna, feminine; ‘width of the outstretched hand’ (from this Italian spanna and French empan, ‘a measure of length,’ are borrowed); allied to spannen, ‘to stretch, expand, span,’ Middle High German spannen, Old High German spannan, strong verb, which corresponds to Dutch spannen, Anglo-Saxon spannan, English to span. The root span, ‘to draw,’ seems to be connected with the cognates discussed under Spanferkel and Gespenst, perhaps even with those of spinnen.