Font sizes in word processing programs and printing presses are measured in points. A point is a unit of length equal to 1/72 of an inch. In the early days of printing, printers defined a font's size as the height of a capital letter. When you design a webpage in HTML, you can also specify font size in pixels. Pixels are not an absolute measure, since their size depends on the monitor's resolution. Knowing how to convert font size to inches is useful if you need to print a poster with large text.
Divide the point size of the font by 72 to convert its height to inches. You may end up with a decimal. For example, if the font size is 100 points, this is equal to 100/72 = 1.3889 inches.
Multiply the decimal part by 16 and round to the nearest whole number. Write this number over 16. This allows you to convert the decimal part to a fraction. For example, (0.3889)(16) = 6, so 0.3889 inches is equivalent to 6/16 or 3/8 of an inch.
Express the final answer as a fraction. For example, 1.3889 inches is equivalent to 1 3/8 inch.
Read your computer's documentation to find the screen resolution of your monitor. Screen resolution is the width and height of the monitor in pixels. For example, if a monitor's resolution is 1,440 by 900 pixels, then there are 1,440 pixels going across the screen left to right, and 900 pixels top to bottom.
Divide the height of the screen in pixels by its height in inches. This gives the number of pixels per inch. For example, if the screen is 900 pixels high and 9 inches high, then the number of pixels per inch is 900/9 = 100.
Divide the font size by the number you calculated in Step 2. This converts font size in pixels to font size in inches. For example, if a font is 25 pixels high, then it is equivalent to 25/100 = 1/4 inch on your computer screen.