Actually the figure keeps getting revised down.
You can check the calcs at NASA website.
Comment by Donald P. Wylie on May 13, 1999
"Interesting example. Regarding the comment at the end that coast lines are not vertical so the estimate of sea level rise is less than calculated, there is a way to estimate a minimum amount of sea level rise. The earth has only 25% of its surface in land above water. If the melted ice sheets covered all land, than the calculation of sea level rise would be reduced by 75%. So the predicted ~80 meter rise in sea level would be ~60 meter if all of the earth's surface were covered with ocean. Therefore, the sea level rise estimate is between 60 and 80 meters. Even 60 meters is a lot in my book.
Expanded on by Claire L. Parkinson Response:
The suggestion made by Donald Wylie is very nice. Elaborating on it, I suggest the following: A lower bound to the amount of sea level rise can readily be estimated by conceptually spreading the water from the ice sheets over the entire globe instead of just over the ocean area of the globe. When this is done, the minimum global sea level rise from the Greenland ice sheet would be (2,343,728 cubic kilometers)/(surface area of the Earth) and that from the Antarctic ice sheet would be (26,384,368 cubic kilometers)/(surface area of the Earth). Inserting the 510,073,000 square kilometer surface area of the globe from the "Hammond Citation World Atlas" (Hammond, Maplewood, New Jersey, 1992, p.352), the results are lower bounds of 4.6 meters of sea level rise from the Greenland ice sheet and 51.7 meters of sea level rise from the Antarctic ice sheet, for a total of 56.3 meters of sea level rise from both ice sheets together."
The agreed up bound is around 61m assuming an ice free world.
