line height

Line height (also called leading, from the lead strips once placed between lines of metal type) is the vertical distance from one baseline of text to the next. It controls how much space separates successive lines within a paragraph.

Line height affects readability directly. When lines are too tightly set, ascenders and descenders crowd each other and the eye has difficulty tracking from the end of one line to the beginning of the next. When lines are too loosely set, the text loses cohesion and the reader’s eye drifts between lines rather than across them.

As a general principle, longer line lengths require greater line height, because the eye must travel farther horizontally and needs a clearer vertical gap to find the next line. Shorter line lengths tolerate tighter spacing. Body text in most contexts reads well at roughly 1.4 to 1.6 times the font size, though the optimal value depends on the typeface, the line length, and the reading context.

In web design, line height is set with the CSS line-height property, which can be specified as a unitless multiplier (e.g., 1.5), a fixed length (e.g., 24px), or a percentage. A unitless multiplier is generally preferred because it scales with the font size of child elements.