I've never seen a "Google" definition of above the fold; however, AdWords offers "above the fold advertising" as an upsell option, which includes the following information:

With so many different web browsers, monitor sizes, and screen resolutions, it's hard to predict where an ad will land, since the same placement may appear in different places on each user's screen. Filtering out below the fold impressions gives you much more control over where your ads appear.

If AdWords can determine dynamic above the fold ad placement one must presume all Google services and algorithms can as well.

Therefore my working belief is that above the fold is treated contextually and not as some hard coded number set.

Thanks.

That kind of lines up with the AdSense warning about not having two ads on screen on mobile and their note about ads moving around on responsive sites and landing in a position that violates the two ads on screen issue.

Makes it hard to plan though.

If you use the Highlander method of ad coding "there can be only ONE!" then you don't have to worry about where the fold may appear.

then you don't have to worry about where the fold may appear.

That's not really accurate.

G disallows large ads, including a 300x250 above the fold on mobile.

There's always someone to spoil a joke. :)

That does beg the question: Is 320x250 BELOW the fold okay? (no!)

If one doesn't know mobile, one should not play in mobile as the big bad G will get ya EVERY TIME! (and that's no joke)

I was looking for actual helpful information, like iamlost provided.

Okay.... as far as I know there is no published dimensions re: what constitutes the "fold" from g, only a list of screen resolutions. It is up to US to check and determine that size (viewport), and make sure things "fit".

Portrait or landscape (just to add a bit of fun)

Thank you

Ken, it's a bit out of date, but I found this 2013 presentation from a Googler about mobile optimization and how they analyze "above the fold"

They don't give any hard numbers as guidance but I think it's helpful at understanding their philosophy on this stuff
[youtube.com...]

Related, I found this:
[paul.kinlan.me...]

That tool is used for optimizing above the fold content, but I think the approach is interesting and related to this discussion. It scans the window height using JS and iterates through every element whose "top" is within the height of the window.

I imagine AdSense uses a similar approach.

That does beg the question: Is 320x250 BELOW the fold okay? (no!)

That's an odd size, but 300 x 250 is certainly allowed below the fold.

Thanks bakedjake.