[aqwwe]

it is probably actually much less then that since Facebook doesn't appear to store full resolutions... for example, they serve a very low quality version of the original picture...

[rhizome]

Yeah, I don't think I see anything larger than (guessing) 600x600px, which they probably compress to ~100k max.

[sp332]

You can download much higher res versions with the Options->Download or Download Full Resolution (depending on platform).