Definition
Leading, pronounced to rhyme with bedding, is the vertical distance between the baselines of consecutive lines of text. The name survives from metal type, where a compositor inserted thin strips of lead between lines of set type to open them up. On the web the equivalent property is line-height, and the two are measured slightly differently: leading traditionally described the added space, while line-height describes the total distance including the type size itself. Line-height is usually expressed as a unitless multiple of the font size — 1.5 means one and a half times the size. Set as a multiple rather than a fixed measurement, it scales correctly when the type size changes, which is why it is the preferred form.
Why It Exists
Leading exists to solve a specific mechanical problem in reading. The eye does not glide smoothly along a line; it moves in rapid jumps called saccades with brief fixations between them, and at the end of a line it must execute a long return sweep to the beginning of the next one. That sweep has to land on the correct line. If the lines are too close, the sweep overshoots or undershoots and the reader re-reads or loses their place, which is experienced as fatigue rather than as a specific error. If the lines are too far apart, the lines stop reading as a connected block and each becomes an isolated stripe. Leading is the setting that keeps the return sweep accurate.
Examples
- →A paperback novel set at roughly 1.4 times the type size, tight enough to keep long pages economical and loose enough for sustained reading.
- →Body text on a content website commonly set between 1.5 and 1.7, because screens and longer measures both need more room than print.
- →A large display headline set at 1.0 or even slightly tighter, since big type needs proportionally far less space between lines.
- →A caption or legal footnote at small size, given generous leading because small type at close intervals becomes a gray mass rather than readable lines.
History
Before leading, there was nothing. Early printers set lines of metal type directly on top of one another, which produced the dense, dark pages characteristic of incunabula, and the practice was called setting solid. As printing matured, compositors began inserting strips of lead alloy, typically one or two points thick, between lines, and the term entered the trade permanently. Because metal came in fixed thicknesses, leading was quantized: a compositor chose one point or two, not 1.37. Phototypesetting in the mid-twentieth century removed that constraint and allowed continuous adjustment, including negative leading where lines could overlap. Desktop publishing after 1985 handed the same freedom to everyone, and the default settings in that software shaped a generation of typography more than any theory did.
In Modern Design
On the web, line-height has become a responsive concern rather than a single value. The comfortable setting depends on three things that change constantly: the type size, the measure or line length, and the typeface's x-height. Longer lines need more leading because the return sweep is longer and harder to aim; typefaces with large x-heights need more because their lowercase letters fill more of the available space. Modern practice therefore defines line-height in a type system as a paired value with each size — tighter for large headings, looser for small body text — rather than setting one global number. Accessibility guidance reinforces this: WCAG's text spacing criterion requires that content remain usable when line height is increased to at least 1.5 times the font size.
Real-World Example
Compare the same paragraph set three ways at sixteen pixels across a comfortable measure. At a line-height of 1.1, the descenders of one line very nearly touch the ascenders of the next, the paragraph reads as a dark block, and the eye repeatedly returns to a line it has already read. At 1.5, the lines are distinct but still visibly belong to one paragraph, the return sweep lands reliably, and the gray value of the block is even. At 2.4, each line floats separately, the paragraph stops cohering, and the reader begins to treat the lines as a list. The content is identical in all three. Only one of them is actually readable at length, and the difference costs nothing to fix.
Key Principles
- →Set line-height as a unitless multiple of the type size so it scales correctly whenever the size changes.
- →Larger type needs proportionally less leading; small type needs proportionally more.
- →Longer measures need more leading, because a longer return sweep is harder for the eye to aim accurately.
- →Typefaces with large x-heights need more leading than those with small ones, so the value belongs with the typeface rather than being universal.
- →The space between paragraphs must be visibly larger than the space between lines, or the paragraph breaks disappear.
- →Leading, measure and type size are a single interlocking decision; changing any one of them requires rechecking the other two.
Why it matters
Leading is the highest-impact typographic setting that beginners most reliably ignore. Text set too tight is the single most common reason a page feels heavy and tiring, and because the problem produces fatigue rather than an obvious fault, readers abandon the text without ever diagnosing why. Correcting it requires no new skill, no design talent and no additional elements — one number changes and the reading experience transforms. It also matters for inclusion. Readers with dyslexia, low vision, or anyone reading in poor light or on a small screen are disproportionately affected by cramped lines, which is precisely why accessibility guidelines set a floor. Getting leading right is one of the cheapest acts of consideration available to a designer.
Then vs Now
Then
Leading was a physical object. A compositor chose lead strips in whole point thicknesses and slid them between lines, so the available values were quantized by what the shop had in its drawers and changing one meant relaying the page.
Now
Line-height is a ratio in a stylesheet that recalculates instantly at every size and viewport width. The freedom is total, which means the defaults in software and the designer's own judgment are now the only things setting the value.
Try it yourself
Take a paragraph of around a hundred and fifty words and set it five times at sixteen pixels, using line-heights of 1.0, 1.2, 1.5, 1.8 and 2.5, keeping everything else identical. Read each one fully and note where your eye loses its place. Then repeat the exercise with the measure doubled and observe how the comfortable value shifts upward. Finally, set a heading at forty pixels and find the point where its leading starts to look loose — you will find it is far tighter than anything that worked for body text. Write down the two values you arrived at and use them as the start of a type scale.