[KDP PUBLISHING] What Size Font is a Large Print Book?

In step one of three one of the questions KDP asks and has a checkbox for says: Large-print book (content is 16 point font size or greater).

So it clearly states the font size in point measurements. So if you want to do a large print book, that is the minimum size to use. You could use 16 or 18 point font. Simply because even though the point measurement system is clear, each font can look a little larger or smaller than another. 

If you click on the last part of the line beside Large-print book it says "What's a large-print book?"

It states this: "Large-print books usually have a font size of 16 points or higher. If you check this box, "Large Print" will appear on your book's Amazon detail page. Checking the box won’t change your book’s font size."