📖 Line Length (Measure) Calculator
Work out the ideal reading width for your body text: set a font size and target characters per line, and get the max-width in px, rem, em and ch — with a live preview and a readability verdict.
Ideal width
594px
37.13rem
CSS max-width
33em
or 66ch (≈)
Readability
Comfortable
ideal 45–75
Good line length keeps the reader's eye from getting lost between the end of one line and the start of the next. Around sixty to seventy-five characters per line is the sweet spot for sustained reading on screens and in print alike.
Long-standing typographic guidance (Bringhurst; usability research) puts comfortable reading at 45–75 characters per line, ~66 being ideal. Set your text container to the width above (using max-width in em/ch keeps it correct if the font size changes). 🔒 Runs in your browser.
How the line length (measure) calculator works
Readability research recommends roughly 45–75 characters per line for body text, about 66 being ideal. The calculator estimates the average character width from your font size (proportional fonts average close to half the font size per character) and multiplies by your target characters-per-line to give the column width, expressed in px, rem, em and approximate ch units, with a live sample at that width.
Set your text container with max-width in em or ch rather than a fixed pixel value, so the measure stays correct if the font size changes. This is a typographic best practice tied to accessibility — the WCAG reading guidance and long-standing typography (Bringhurst) both point to keeping lines from running too long, which is where the eye gets lost jumping back to the next line.
Frequently asked questions
What is the ideal line length for reading?
About 45–75 characters per line for body text, with roughly 66 as the sweet spot. Shorter lines feel choppy; longer lines make it hard to find the next line. This tool converts that target into a column width for your font size.
What CSS should I use to limit line length?
Set max-width on your text container. Using em or ch units (e.g. max-width: 66ch) keeps the measure correct even if the font size changes, which fixed pixels don't.
What is a ch unit?
1ch is the width of the "0" glyph in the current font. It's a handy unit for line length because a max-width in ch maps almost directly to characters-per-line.
Does line length really affect readability?
Yes — overly long lines tire the eye and cause it to lose its place returning to the left margin; overly short lines break reading rhythm. Keeping within ~45–75 CPL measurably helps comprehension.