An Etymological Dictionary of the German Language/Spanne
Spanne, f., ‘span,’ from MidHG. spanne, OHG. spanna, f.; ‘width of the outstretched hand’ (from this Ital. spanna and Fr. empan, ‘a measure of length,’ are borrowed); allied to spannen, ‘to stretch, expand, span,’ MidHG. spannen, OHG. spannan, str. vb., which corresponds to Du. spannen, AS. spannan, E. 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.