Because of the variation in screen resolutions, screen font sizes are discussed in terms of screen line sizes, not typographic point sizes. The equation for relating point size to equivalent screen line size is as follows:
<$Escreen~line~size~=~ { text~point~size~ times ~lines-per-inch } over 72>
The lines-per-inch value specifies the logical page size for the device. When possible, the lines-per-inch closely matches the physical size and aspect ratio. The common screen lines-per-inch sizes for devices supported by Windows are as follows:
For a 1:1 aspect ratio, 96:96 (VGA), 108:108, 120:120 (8514/a), and 144:144
For a 4:3 aspect ratio, 96:72 (IBM Enhanced Graphics Adapter)
Since it is always better to select a smaller size when an exact match is not possible, the quotient in the equation is truncated if the result is a fractional line size.