The average ocean depth is 4.3 kilometers (2.65 miles)

The Spanish Dancer, a type of sea cucumber, hovers at 2,789 meters (9,150 feet) near the Davidson Seamount off the coast of California. That's 1.7 miles down!

The average depth of the ocean is about 4,267 meters (14,000 feet). The deepest part of the ocean is called the Challenger Deep and is located beneath the western Pacific Ocean in the southern end of the Mariana Trench, which runs several hundred kilometers southwest of the U.S. territorial island of Guam. Challenger Deep is approximately 11,030 meters (36,200 feet) deep. It is named after the British survey ship Challenger II, which first surveyed the trench in 1951.

For more information:
Soundings, Sea-Bottom, and Geophysics, NOAA's Ocean Explorer