This month, researchers made official something that typeface
designers have long known: that horizontal lines appear thicker
than vertical ones. At left, a square made from equally thick
strokes; at right, the one that feels equally weighted, its
vertical strokes nearly 7% thicker than the horizontals. This
phenomenon, central to typeface design, has implications for the
design of logos, interfaces, diagrams, and wayfinding systems,
indeed anywhere a reader is likely to encounter a box, an arrow,
or a line.
Published in the journal Vision, this peer-reviewed paper
confirms that most people overestimate the thickness of horizontal
lines. This is the very optical illusion for which type designers
compensate by lightening the crossbar of a sans serif H, an
adjustment that’s easily revealed by looking at a letter sideways.