What are the current usability guidelines for the size of buttons (or anything clickable) on web pages?
there are no "official" guidelines for this, so i would recommend to simply take a look at some famous sites. lets's take SO as an example - it wouldn't be such popular without:
- a good, easy to use and easy to understand ui
- the main-menue consists of only few points, so nobody gets confused
- the buttons are big, so the're easy to click, but not too big (they don't force you to move your mouse too far)
- the font-size is nice, a bit taller than the normal text to be apparent and with a good contrast to the background for easy reading without hurting your eyes
- the site itself is light and bight, the text is black on white (good contrast again, for a lot of text this is better than withe on black (in my opinion))
Someone asked a question about the size of clickable elements and no one has mentioned Fitts's Law?
All other considerations aside, Fitts's Law says (aproximately) "Bigger is better, but you'll get more return from changing from small to medium than medium to big.)
As large as possible. The larger a clickable item is, the easier it is to click on.
There are of course other factors that conflict with this, like that you want to have room for other things than just buttons...
One thing to consider is if you'll be aiming to add touch capabilities to your site. If so, that's a factor to take into consideration. On a touch device you'll want more space between buttons and, ideally, larger buttons (or at least larger target areas)
IF you wish to follow Windows UX guidelines, there are indeed guidelines for the size of the button. This can be replicated to Web applications. But not sure if you would do that for web pages. 23px is what windows UX guidelines say