From the web site about
Toba
"Bill Rose and Craig Chesner of Michigan Technological University combined all the information on the extent of the Toba volcanic material to deduce that the total amount of erupted material was about 2,800 km3. About 800 km3 was ignimbrite that travelled swiftly over the ground away from the volcano destroying everything in its path, and the remaining 2,000 km3 fell as ash, with the wind blowing most of it to the west. Such a huge eruption probably lasted nearly two weeks. Very few plants, animals or humans around this part of Indonesia would have survived."
The 2,000km3 of ash converts to 479 cubic miles. That compares to 240 cubic miles from the last Yellowstone Caldera eruption stated in the USGS website.
(:raig