As you might have guessed, most designers choose this unit arbitrarily. The problem with this approach is that the resulting baseline grid unit is not directly related to the primary font size, which is the most fundamental design element on the page.
Instead of relying on arbitrary selection, wouldn’t it be nice if there were a way to determine the perfect typography settings based on a given context?
As it turns out, the golden ratio provides us with a guide—a formula—for proper typesetting. Because of this, we can now set our type with absolute certainty in any situation! Better still, we can use this information about typography to make more informed decisions about all the spatial aspects of our designs, such as: