Reading Width Calculator
Turn your font size and a target line length into the ideal content column width in pixels.
How it works
Line length matters more than most people think. Lines that run too wide make the eye lose its place jumping back to the start; too narrow and reading becomes choppy. Typographers put the comfortable range at roughly 50 to 75 characters per line.
To turn a character count into a pixel width you need the average character width, expressed in em. For typical body fonts that's around 0.5em — meaning each character takes about half the font size in width. Multiply characters by that width by the font size in pixels.
So at an 18px font, 66 characters per line, and 0.5em per character, the ideal column is about 66 × 0.5 × 18 ≈ 594 pixels. Set your content wrapper to roughly that and paragraphs stay easy on the eye.
Frequently asked questions
What's the ideal line length for reading?
About 50 to 75 characters per line, including spaces, with 66 often cited as the sweet spot for body text. Shorter suits narrow columns and mobile; longer starts to tire the reader.
What is the average character width in em?
It varies by typeface, but 0.5em is a solid default for most proportional body fonts. Condensed fonts run narrower, around 0.45em, and wide or monospaced fonts run closer to 0.6em.
Should I set my width in px, em, or ch?
The CSS ch unit is built for exactly this and ties width directly to character count, so max-width in ch is the cleanest approach. This tool gives px, em, and rem so you can plug the number into whichever your layout uses.