A full cup

Hi,

When a mitzvah requires a blessing on a cup of wine, such as Sheva Berachot, we require that the cup be filled to the top.

(Rav Moshe Feinstein, Igrot Moshe Orach Chaim 4:70:10)

[I sense that "full" is defined based on whether people who see it call it "full", rather than a particular measure of distance from the top, but I cannot prove this.]

Have a great day,
Mordechai