Vertical Rhythm
Set every line and space to a consistent baseline interval, and the page feels even instead of lumpy.
A steady cadence
When line-height and spacing are multiples of one base unit, text settles onto a shared rhythm.
The eye stops noticing the spacing and just reads.
Measure
Line length governs reading comfort. Too short and the eye jumps; too long and it loses the return. Aim for roughly 45–75 characters.
A comfortable line length lets you move from one line to the next without losing your place or rereading. Too short and the eye keeps jumping back; too long and it struggles to find the start of the next line.
Scale & Hierarchy
Sizes drawn from one ratio create harmony and instant hierarchy. Flatten them and everything competes for the same attention.
Leading
Line spacing decides whether body text is comfortable or cramped. Cramped lines blur together; over-spaced ones break into stripes.
Leading is the space between lines of type. Set it well and paragraphs read as a single, continuous flow; set it poorly and the reader works to keep their place. For body copy on screen, somewhere around 1.5 to 1.6 tends to feel right.
The Grid
A shared column structure aligns every element and saves you re-deciding spacing on every screen.