Put one paragraph in three different boxes. Set leading narrow in one and wide in another, making the spacing clear to separate the lines. In the last box, keep the leading in between the two. Then read each text box without zooming, from the standard size on the computer. Now the leading will no longer be a number from a menu; it will be visible and will be something you can actually do with your design.
Leading (the spacing from one line to the next) determines the vertical space between lines of text. Too little leading creates crowded letters and makes it harder to follow a paragraph. When the paragraph gets very tight the ascenders and descenders look crowded, which can make it difficult for readers to find the start of the next line. A paragraph may look “heavy” or dark even though the text is the correct typeface and size, or is suitable in size for its content, depending on the leading setting. It is most noticeable in lines that are very long, in small text sizes, or in type that has letters that go very far beyond the x-height (the letters ascenders and descenders).
But too much leading creates a whole new set of problems. Now the lines look like they belong to different paragraphs. When reading, the eye has to travel a long way to find the next line, which may disrupt the continuity of the paragraph or the sentences. Text with excessive leading may look very spacious from a distance, but it may appear slow or disconnected while reading the text on the computer or printed page.
The correct setting for a certain typeface can differ depending on font size, x-height, ascender, descender, leading and line length. A font with a very tall x-height will look full and may need more leading for it to work in an appropriate proportion. Also, a font family with very long ascenders or descenders may look tighter than other text at the same leading value. Lines that are wider will often require slightly more leading since the eye has further to travel to the next line.
Change leading and nothing else (no typeface, text size or width, and no leading between lines/paragraphs). Try changing the leading at small steps and comparing the text side by side with your eyes. Check the actual space between the lines, not just the values provided by the computer. While the lines need to look like they belong to one line of a paragraph and they shouldn’t separate completely, each line needs to be legible and easy to spot.
The paragraph spacing is not to be confused with paragraph spacing. Adding space between the lines is not the same as adding space between different paragraphs. It is best to make every single paragraph have a uniform and even spacing within it and then decide if that paragraph should have space before or after it, which is the paragraph spacing. This way your text is well-spaced and structured, but it won’t be too messy when you’re reading through it.
Check the text where the reader will most likely see it (screen, printed page). When looking at the screen or printed version, take a few steps away from it, and then check to see if it’s easy to follow the reading of text without struggling to find the beginning of the next line, or having a good read across. Good leading will not seem to call attention to itself, but instead the lines will just seem to fit, and the paragraph won’t look tight or have gaps that are too big to leave lines to breathe on their own.