The query "how deep is" is incomplete, and the most relevant information based on popular searches is related to the song "How Deep Is Your Love" by the Bee Gees and Calvin Harris & Disciples. The phrase "How deep is your love?" is famously known as a song title and lyric from the Bee Gees' 1977 ballad, which was part of the "Saturday Night Fever" soundtrack. The song explores themes of love's depth and devotion metaphorically, comparing love to the vastness of the ocean and the heights of nirvana. It reached significant chart success and remains a classic favorite.

If the question was about actual physical depth (e.g., ocean depth, scientific context), please provide more specifics for a targeted answer. Otherwise, this phrase is chiefly associated with the song and its lyrical meaning about emotional depth.