---
name: Ch unit
slug: ch-unit
category: typography
status: published
created: 2026-08-21T00:00:00.000Z
modified: 2026-08-21T00:00:00.000Z
definition: A CSS length equal to the advance width of the digit zero in the
  current font, used to set column widths in characters rather than pixels.
aliases:
  - name: character unit
    source: css
  - name: ch
    source: css
  - name: character width unit
tags:
  - spacing
  - web-platform
relations:
  contrastWith:
    - measure
    - em-unit
  variantOf: []
  partOf: []
  seeAlso: []
implementations: []
sources:
  - title: Line Length (Measure)
    url: https://kweri.app/learn/line-length-measure
demo: inline
exhibit: false
useWhen: setting a column width in characters, not pixels
---

`1ch` is the advance width of the digit zero in whatever font is in effect on that
element. Not the average letter, not the widest one: the zero, specifically, and the
advance rather than the ink, so the sidebearings are included. The unit exists
because the constraint typographers actually care about is stated in characters.
[Measure](/measure) is a count of characters per line, so `max-width: 66ch` writes
the rule down in the units of the rule itself, and the column then tracks any
change in type size for free.

The reason it is the zero and not something more representative is practical: in
almost every font the digits share one advance, so the zero is the most stable
single glyph to hand to a layout engine. In a [monospace](/monospace) face that
makes `ch` exact, and `40ch` holds exactly forty characters of anything. In
proportional text it makes `ch` an approximation, and a generous one, because a
zero is wider than an average lowercase letter and much wider than a space. A
66ch column of English prose typically fits closer to 75 characters, which is why
about 60ch usually lands on the measure you were aiming for.

The unit is font-relative and font-specific, which is the part that surprises
people: it is not just proportional to the type size like [em](/em-unit), it also
changes with the family. Set the same `45ch` in two faces at the same size and you
get two different pixel widths, because their zeros are drawn to different widths.
So a column sized in `ch` survives a size change intact and does not survive a
font swap intact, and a webfont arriving after first paint can visibly resize a
column that was laid out against the fallback. Newer siblings fill the gaps for
other axes: `cap` and `ex` for vertical measurements, `lh` for a line's own
height, and `ic` for the advance of a full-width CJK glyph, where a zero says
nothing useful.