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Font anatomy

Lesson 06 · 3 min read · Updated 30 September 2026

Type designers have a name for every part of a letter. Pick a part below to light it up in Instrument Serif, the site’s own serif, then read what it does.

Fig. / Hoped in Instrument Serif

510 units · 51% of the em

Read the letter

The x-height.

The height of the lowercase without its ascenders, measured on the x. It sets how big a font looks.

Lines
Strokes
Spaces

01

The lines letters stand on

Letters sit on the baseline. The x-height is the height of the lowercase without its ascenders, measured on the x; the cap height is the height of flat capitals such as H. Ascenders rise above the x-height, in b, d, h, k and l, and descenders drop below the baseline, in g, j, p, q and y. In Instrument Serif the x-height is 51% of the em, the font size, and the cap height 72%; the d’s ascender reaches a little higher than the capitals, to 74%.

The x-height does more than any other measure to set how big a font looks. At the same size, Inter’s lowercase stands 35% taller than EB Garamond’s, so Inter reads larger and EB Garamond more delicate. Across the fonts on FontKind, half have an x-height between 47% and 53% of the em.

Hxgp in EB Garamond. Lines at the measured heights, as a share of the em
Hxgp in Inter. Lines at the measured heights, as a share of the em

02

Strokes

The stem is a letter’s main upright stroke: the sides of H, the upright of d. A bowl is a curved stroke that closes a space, as in p and d. A bar, or crossbar, is a horizontal stroke, as in H, A and e. Serifs finish the ends of strokes, and a terminal is a stroke end without one, such as the tail of the e or the upturned foot of the d.

Letters have more parts than these: the arm of an E, the leg of an R, the spur of a G, the ear, link and loop of a two-storey g. The names matter because fonts differ in them, and a single one can give a font away.

03

Spaces

A counter is the white a letter encloses, fully in o and d, partly in c and n. The aperture is the opening of a partly closed counter, such as the mouth of the e or the c. Open apertures keep letters apart at small sizes and on poor screens, which is why fonts made for reading keep them wide; closed apertures, as in Helvetica, look tidy and firm.

Counters shape the rhythm of text as much as strokes do. Type designers space letters so that the white inside and between them reads as one even texture, which is why kerning works on the gaps, not on the letters.

04

Why round letters overshoot

Round and pointed letters are drawn slightly past the lines: the o rises above the x-height and dips below the baseline, and the O goes past the cap height. Drawn exactly to the lines, they would look too small, because a curve touches a line at one point where a flat letter meets it along its whole width.

The correction is small. Instrument Serif’s o overshoots by 6 thousandths of an em at the top and 9 at the foot; DM Sans Bold draws its O 3.4% taller than its H. Pick overshoot on the board to see it through the loupe, then judge one yourself in the balance test.

05

Try it in the game

06

Fonts to open

Serif fonts Sans serif fonts

07

Questions

What is the x-height of a font?
The height of its lowercase letters without ascenders or descenders, measured on the x and given as a share of the font size. Half the fonts on FontKind fall between 47% and 53% of the em.
What is the difference between a counter and a bowl?
The bowl is the curved stroke that encloses a space, as in b, d, p and q; the counter is the space itself.
What are the parts of a letter called?
The main ones are the stem, bar, bowl, arm, leg, serif and terminal, the counter and aperture they enclose, and the ascender and descender, measured against the baseline, x-height and cap height.

08

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