How is sea level rise due to a glacier melting calculated?

There's news going around (e.g. link) that the melting of the Thwaites glacier may cause sea levels to rise by 10 feet. Is that true and not exaggerated? How is the calculation made? They said the glacier is the size of Florida so I'm looking at a world map but having trouble imagining a mass that small (compared with the rest of the Earth) can affect such a large surface area of water by that much.

From the link in case the article disappears:

This makes the ice shelves on Thwaites and Pine Island more sensitive to extreme climate change in the ocean, atmosphere and sea ice. If Thwaites and Pine Island were to destabilize, several of the neighboring areas would also fall apart, causing a widespread collapse, the scientists said. Thwaites alone could cause sea levels to rise about 10 feet, the scientists said.

To attempt a back of the envelope calculation (and show some effort): The surface area of the Earth is said to be about 510 million km^2, 71% of it water as opposed to land, so 362 million km^2. This times the sea level change of 10 feet (0.003048 km) yields a volume of 1.1 million km^3. The Thwaites glacier's basin area is said to be about 192,000 km^2. (I know I haven't accounted for the difference in volume of liquid water versus ice, and probably other factors, but I'm just trying to see if the answer is within an order of magnitude of what makes sense to me.) To have a volume of 1.1 million km^3 with a basin area of 192,000 km^2, the glacier would have to be over 5 km in height. That's more than 10 Empire State Buildings, or nearly twice the Burj Khalifa, in height. Are glaciers actually that massive? I can't seem to find out the height of this glacier anywhere for some reason. Probably for a good reason (it's complicated).

• If you follow the links in the news story to the original article you will see that the scientists never suggested that a collapse of Thwaites in itself would cause metres of sea level rise. The '10 foot rise' statement is a hypothetical if the removal of Thwaites was to allow major movement and melting of the much much larger West Antarctic ice sheet Sep 7, 2022 at 8:46