How to use the line length and measure calculator
A measure that runs too wide loses the eye on the way back to the next line; one that runs too narrow breaks the text up with constant wrapping. This calculator takes a font size, an average glyph advance and the character target you set, returns the measure that holds that many characters in px and em, and writes the max-width CSS you can paste.
The formula is measure = target characters x average advance (em) x font size (px). Add your current measure and it works backwards to how many characters that width holds and reports the gap to one decimal. The ch figure is based on the advance of the zero glyph, so it appears only when you supply that. Written as of October 2026.
The 45 to 75 character range is a widely quoted figure, not an authoritative standard. The sources behind it differ, so this tool does not judge against that range and compares only against the target you entered. Letter spacing, word spacing, line height and side padding are not modeled and no font size ceiling is applied, so check the result with your real copy in place.
Frequently Asked Questions
No. The 45 to 75 character range for Latin text is widely quoted but the sources disagree, and Korean or Japanese glyph widths make it inapplicable. Set your own target and this tool converts it into px.
Set a line of 100 characters in the font you are using, divide the total width by 100, then divide by the font size to get the em ratio. Full-width Korean sits near 1, while Latin fonts differ enough that measuring is worth it.
In CSS, 1ch is the advance of the zero glyph, which does not match the width of the text you are setting. The ch figure therefore appears only when you supply that advance, and the main results stay in px and em.