Make sure they take no more than 15% of the screen, and are
easy to dismiss.
Actually, Google now penalizes intrusive popups on mobile, and
so it is recommended to keep them to maximum 15% of the
screen, and make them easy to dismiss.
To be more precise, read Google’s original announcement about
So there are some cases where large popups on mobile are still
ok, for instance to accept cookies or to have the user log in.
Otherwise, keep the popup size to about 15%.