Font size doubts (for webdesign)

Is f开发者_JAVA百科ont size = 12.5 pixels the same as font size = 13 pixels?

The screen obviously can't render half a pixel, so I would assume in most browsers yes it would round up to 13px.

In what context? Fonts are usually stored using vectors so the output context affects rendering, not the font itself.

EDIT: Since you changed the title to specify web design I'd have to say again it's browser dependent. The CSS spec does not appear to say.

http://www.w3.org/TR/REC-CSS1/#length-units

Don't think so. You can test that when zooming in. Put 2 texts beside each other and then zoom in at least 200% (800% would make the difference more noticeable though). It might also affect how the letters are drawn when anti-aliasing is on in the browser (on by default for most of them).

Edit: I've used this with "em"s and having X.Y pixels per em instead of round(X) made a difference (because child nodes in the HTML DOM that inherited the em size from above scaled the text and other stuff according to the precise value, not the rounded one). On 100% zoom level it might not make that much of a difference.