Leading (pronounced ledding) refers to the amount of space between the lines of type, and it is an important tool for improving readability.
It is set automatically by your software, but it can be adjusted. The default setting usually makes the leading 20% greater than the point size of the body text. In other words, a 10 point font will have a twelve point leading. In One Minute Designer, Roger Parker offers very useful guidelines.
- Long lines of text should have more space between them.
- Short lines of text should have less space between them.
- In longer lines of text with generous leading, set the body typeface at 11 or 12 points.
- In shorter lines of text with less leading, set the body typeface at nine or ten points.
- Create a template: take a column of text and set it with the standard 2 point difference between type size and leading. Then set the same column of text with a half point less leading, and then again decreasing the leading by a full point. Look at these side by side to see which is more readable.
- Improve the readability of sans serif body text by increasing the leading.
- Tall x-heights need more leading because the ascenders and descenders are shorter and have less surrounding white space.
- Short x-heights require less leading because the tall ascenders and low descenders build-in white space.
The main reason for adjusting leading is to improve readability. Generally speaking, narrow columns should have a smaller typeface and less leading, and wider columns should have a larger typeface and more leading.
Finally, keep in mind that by reducing the space between lines of text, the page will become darker, so you should add white space in other places.