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.)