Is decimal precision in determining the font size followed by all browsers?

Question

If I use the following CSS:

p { font-size: 20.5px; } 

Will all browsers draw this as 20.5px, or will they be around the value?

Answer 1

Decimals are not rounded sequentially in all browsers. The best post I could find is here: Rounding the Browser

It contains a table that shows the following:

 Internet Explorer 7 truncate to 2 decimal places Internet Explorer 8 truncate to 2 decimal places Internet Explorer 9 truncate to 2 decimal places Internet Explorer 10 truncate to 2 decimal places Internet Explorer 11 truncate to 2 decimal places Firefox 3.0 truncate to 3 decimal places Firefox 3.5 truncate to 3 decimal places Firefox 31 truncate to 3 decimal places Chrome 20 round to 15 decimal places Chrome 21 round to 15 decimal places Chrome 37 round to 13 decimal places Safari 6 (OSX Lion) round to 15 decimal places Safari 6.1 (OSX Mountain Lion) round to 15 decimal places Safari 7 (OSX Mavericks) round to 15 decimal places Mobile Safari 7 (iOS7) round to 15 decimal places Mobile Safari 8 (iOS8) round to 15 decimal places Chrome 36 (Jelly Bean) [Nexus5] round to 15 decimal places Chrome 30 (KitKat) [S5] round to 15 decimal places Android Browser 4 (Jelly Bean) [Nexus7,Nexus4,S4,S3] round to 15 decimal places Android Browser 4 (Ice Cream Sandwich) [Nexus,KindleFire2] round to 15 decimal places Android Browser 4 (Gingerbread) [S2] truncate to 3 decimal places Opera 12 truncate to 2 decimal places Opera Next 24 round to 13 decimal places 

Answer 2

All recent browsers allow subpixel rendering * . See the study and the table of differences between browser versions .

Older browsers are mostly around pixels down. The most notable exceptions are IE8 and IE9, which are rounded to the nearest integer (IE7 also rounds, IE10, and before using subpixel rendering).

_{* If you specify the size as a percentage, the value in pixels may differ, as if directly determining it in pixels.}