Supervolcanoes are big enough to make the normal volcanoes look like harmless fountains. There are six known supervolcanoes: the Yellowstone, Long Valley, and Valles Caldera in the United States; Lake Toba, North Sumatra, Indonesia; Taupo Volcano, North Island, New Zealand; and Aira Caldera, Kagoshima Prefecture, Kyūshū, Japan.
A supervolcano is capable of producing a volcanic eruption with ejecta greater than 1,000 cubic kilometers (240 cubic miles). Comparing it to Mount Pinatubo, the biggest volcanic eruption in almost 100 years. Pinatubo erupted with ejecta of roughly 10 cubic kilometers and that's a LOT for a normal volcano.
Documentary, Mega Disasters - Yellowstone Eruption