32 million men.
Fascinating article from the New Yorker:
"In battle, a historian wrote, “the Mongols made the fullest use of the terror inspired by their physique, their ugliness, and their stench.” Mongols were narrow-waisted and small-footed, with big heads. They shaved their hair short on the backs and tops of their heads and left it long at the sides. Custom forbade them from ever washing their clothes. Also contributing to their smell might have been their diet, which at certain times of the year was mainly mare’s milk. On marches when there wasn’t time to milk, Mongol riders would open a vein in their horses’ necks and drink the blood, either straight or from a pouch. Mongols were especially fond of fermented mare’s milk, called kumis. Many Mongol nobles died young from drunkenness. After victories, Mongols sometimes celebrated by drinking kumis while sitting on benches made of planks tied to the backs of their prisoners."
http://www.newyorker.com/printables/fact/050425fa_fact4