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About this tool
Calculate a comfortable line height from font size and measure width, with characters per line and WCAG checks.
Line Height Calculator recommends leading from the two things that actually determine it: the font size and how wide the column is. It converts the column width into characters per line (measure ÷ average glyph advance), then adjusts a role-appropriate base ratio upward for long lines and downward for large type, because longer lines need more leading to guide the eye back and larger type already carries a bigger gap. It also reports whether the measure sits inside the 45-75 character band and whether the result clears the 1.5 line spacing WCAG 2.x SC 1.4.8 asks for in body text.
Open Line Height Calculator on AltFTool — it loads instantly in your browser.
Enter the values you already know.
Fine-tune the options to match your scenario.
Read the result and use it in your planning or reporting.
Leading rises with characters per line instead of applying the same 1.5 to every column width.
The result is also snapped to your grid unit, with the effective ratio that produces.
Body text below the 1.5 WCAG line spacing minimum is called out rather than quietly shipped.
Around 1.5 for a comfortable measure, rising toward 1.7 for long lines and falling toward 1.4 for narrow columns. WCAG 2.x SC 1.4.8 sets 1.5 as the minimum line spacing within paragraphs for the AAA level, so 1.5 is a sensible floor for running text.
45 to 75 characters is the long-standing range for a single column of running text, with about 66 as the ideal. Below 45 the eye jumps lines too often; above 75 it struggles to find the start of the next line, which is exactly when extra leading helps.
Use a unitless number for body text so it scales with the font size and inherits sensibly into nested elements. Use a pixel value only when you are locking text to a baseline grid, and be aware it will not adapt if the font size changes.
No. Headings and display type are usually set between 1.0 and 1.25 because the leading gap grows with the font size, so the same 1.5 ratio would leave a large headline looking loose and disconnected.
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title="Line Height Calculator — free AltFTool widget"
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loading="lazy" referrerpolicy="no-referrer-when-downgrade"></iframe>
<p style="font-size:12px;margin:4px 0 0">Widget by <a href="https://www.altftool.com/tools/all/line-height-calculator?utm_source=embed&utm_medium=widget">AltFTool — free online tools</a></p>