Sub-pixel Fonts in IE9

Older versions of Internet Explorer use whole-pixel text metrics in which font sizes, character widths, and line heights were all rounded to the nearest pixel. For example, with IE8 if you ask for a font size of 10pt, you get a 13 pixel font size, even though a mathematically accurate conversion of points to pixels yields a 13.333 pixel font size. The following table illustrates this for common font sizes specified in points.

Point size requested	Precise pixels	Rounded pixels	Point size you got in IE8	Font size change in IE9
8pt	10.67px	11px	8.25pt	Smaller
9pt	12	12px	9pt	None
10pt	13.33px	13px	9.75pt	Larger
11pt	14.67px	15px	11.25pt	Smaller
12pt	16.px	16px	12pt	None
14pt	18.67px	19px	14.25pt	Smaller
16pt	21.33px	21px	15.75pt	Larger
18pt	24px	24px	18pt	None

In IE9’s default standards mode, you get what you ask for: ask for 10pt, you get 10pt (13.33 pixels), slightly larger than what you got in IE8 and before. Similarly, 8pt ends up a quarter of a point smaller in IE9.