The size of characters in a font is usually measured in points, where a printer's point is 1/72 of an inch. So the tall characters in a 12pt font are around 1/6 of an inch high, whereas a 14pt font is about 1/5 of an inch and 7pt font is about 1/10 of an inch. However, the exact size does vary between fonts. On screen the physical size of pixels (the screen resolution) varies. Old displays often used to have around 70 pixels per inch, so a point and a pixel were nearly the same, but now that varies a lot more, particularly for phone displays and retina displays. The device tries to choose a pixel-height that closely matches the paper dimensions of the desired font. If the precise screen size of characters matters, the font size may be measured in pixels.

Used on pages 137, 138