Leading means: the height from the baseline (bottom) of one line of text to the baseline of the next line of text. Some people, especially digital-first people, call this “line height.” The term leading actually comes from the days of letterpress printing, in which every empty space was actually a physical piece of metal that had to be inserted; thus, adding height to a line of text meant adding a long, thin piece of metal called a lead.
Anyway, if your leading is too large, the lines of text will be too far apart and the color of the page will get too light and airy, with large strips of white space separating the lines of text.
If there’s not enough leading, the spaces between the words (word spaces) will look large and distracting. It will also be difficult for the reader to go from line to line without getting lost.
A general guideline is to set leading to 1.2X the point size. So if your type is 10pt, then use 12pt leading. This is written 10/12 and said “10 on 12.”
Note: 1.2X is a rough estimate. In truth, the correct leading depends largely on x-height (the height of lowercase letters) and measure (line length).
You may have noticed that some fonts look bigger than others at the same point size; this is usually a result of larger x-heights. The larger the x-height, the more leading that’s needed. Some typefaces have a short x-height, so you can get away with setting them 10/10 or 10/11. Others just look tall and need extra room: 10/13 or 10/14.
Also, the longer the measure (the longer the lines of text) the more lead. It becomes difficult to find the start of the next line if all the lines are long and close together. Think of how books and newspapers differ here. (Thanks Richard Hunt for the pointer!)
In Microsoft Word, click on the line-spacing button, where you can select from the preset line-heights. Then select “Line Spacing Options…” Then, under Spacing, select Multiple, and enter the number you’d like (1.2 here).
In Adobe programs, you’re looking for the Character Panel, which you can usually find under “Window.” Then, once you have the character panel open, adjust leading with the little area that shows the distance between two baselines (line height).
When designing for the web, you’re going to use the CSS:
Element selector {
line-height: 1.2em;
}
