Counter

A counter is a piece of letter anatomy: the white shape a stroke encloses, the ring inside an o, the space inside the bowl of a b or a p, the loop of a g, the lens above the crossbar of an e. It has nothing to do with a character counter under a text field, and nothing to do with the CSS counters that number a list. Typographers talk about counters because the white is drawn as deliberately as the black: a designer fitting a family decides the counter’s shape first and lets the strokes fall around it, which is why a face with generous counters reads well small and a face with mean ones goes muddy.

Weight is what a counter is most sensitive to. Raise the weight of a face and the outer contour barely moves while the strokes thicken inward, so the counter is what gets spent. That is the real limit on a black weight: not how thick a stem can be drawn but how small a counter can get before the letter stops being distinguishable, which is why the heaviest cuts of a family often widen every letter to buy the enclosed space back. The same trade sets the relationship between counters and x-height, since a large x-height at a given size is mostly a way of paying for larger counters, and it is one of the few concrete things behind an otherwise vague judgement about legibility. Increasing font weight in an interface is therefore not a free emphasis: at small sizes it is a decision to trade counter for colour.

The word to keep it apart from is aperture, the other anatomy term about openings, and the distinction is exact. A counter is enclosed, fully shut in by strokes. An aperture is the gap where a stroke stops short instead of closing, the mouth of a c, the opening of an S, the space between the terminals of an a. One letter routinely has both: the upper part of an e is a closed counter and its lower part is an aperture, and closing that aperture too far is the classic way to make an e read as an o at small sizes. Where a designer widens apertures for the same reason they enlarge counters, the two are working together; where an aperture is closed to tighten a rhythm, they are in competition.

The specimen on this page fills each enclosed space with a solid tint, which is a teaching device rather than how anyone sets type, and draws the letters as vector paths rather than setting them in a face, so that the same three weights differ in exactly one variable. Look at what the fill does: once it is a shape, the counter stops reading as absence and starts reading as one of the forms the letter is made of, which is the way anyone who draws type sees it already.