When working with fonts or typefaces, size is measured in points. Page layout settings like column width and the space between lines (leading) are measured in picas. Here is an explanation of the two measurements:
Points and picas are a measurement system just like inches and feet. Twelve points equal 1 pica. There are 6 pica or 72 points to an inch. A typeface is measured in points from the top of an asender (like a lowercase d) to the bottom of a desender (like a lowercase g) based on the lowercase alphabet.
You may have heard the term x-height. It represents the measurement of the body of the lowercase letter such as the round part of an a, d or g. Many letters like an “x” have neither an asender, nor a desender, so the x-height represents the whole lowercase letter. Capital letters for each typeface are generally the same height. They typically are the height of the body and asender of the lowercase letter, so they are about 2/3 of the lowercase letter height.
When I receive orders for solar and electrical signs, all caps Arial (Helvetica) is specified, and a letter height in inches is typically requested. Translating this to points, I get a different point size than the 72 points to an inch because they are all caps. For all caps Arial, roughly 100 points is an inch. It makes it easy to remember as 50 points is then a half inch and 25 points is a quarter inch.