In the end of the movie, they find Dryland, which turns out to be the peak of Mount Everest, still above sea level. If I remember correctly, the narrator say it, literally, in the end of the movie. The alternate version indicates it differently:
For the first airing on ABC which restored footage cut from the film, we see Helen and Enola standing atop the cliff watching the Mariner depart before the film's end credits. As they are standing there they uncover a plaque which tells us that they are at the peak of Mt. Everest.
Finally, Enola's tattoo also indicate Mount Everest :
The characters inside of the circular part is longitude & latitude's actual coordinates.
Latitude = 27° 59' N
Longitude = 86° 56' E
Spoiler alert: it is the location of Mount Everest.
According to Wikipedia's List of highest mountains, it peaks at 8,848 meters (29,029 ft) above sea level and the runner up is the K2 at 8,611 meters (28,251 ft).
So we could assume the sea raised more than 8,611 meters, but less than 8,848 meters.