X-height: how tall the small letters are

How font.io measures x-height — the median body height of five lowercase letters, which decides how big a font reads.

Inter: 0.555. Bodoni Moda: 0.46. X-height is the height of the main body of the lowercase letters — the x, a, e, n, o, the letters without tall ascenders or deep descenders — as a share of the font’s size. It’s the number that decides how big a font reads at small sizes: a large x-height looks bigger at the same point size.

X-height: the body of x, a, e

Inter — rules sit at each glyph’s measured body top and bottom (longest run of rows carrying ≥30% of max row ink)

The median over x/a/e/n/o (whichever exist) rejects a single swashy outlier. This outline-based pass agrees with measure.py to the third decimal.

The measurement: take the x, a, e, n, and o, measure each one’s body height, and take the middle value — the median. The median matters because it can’t be dragged around by one oddball: if four letters agree and one is a swashy outlier, the outlier loses the vote.

A real example: Inter’s five letters center on 0.555. Bodoni Moda’s center on 0.46 — noticeably smaller-bodied, part of why Didones can look petite next to a grotesque at the same size.

One caveat: if the five letters wildly disagree with each other — the ransom-note end of type design — there’s no meaningful single number, so we flag it instead.