Sauron's Armies

[The Sixth Wizard]

I don't think there could possibly be that many orcs at the 'book' Pellennor Fields, simply because it would be impossible to win the battle. 6,000 Rohirrim, the garrison in Minas Tirith (which we don't know the number), 3,000 or so reinforcements from Dol Amroth, and a couple of hundred northern Rangers (in the book there was no Army of the Dead at the actual battle of Minas Tirith, they had fulfilled their oaths killing off the Corsairs). All in all not many, considering there were nine Nazgul, heaps of Mumakil and countless Trolls and Orcs against them. So I'd say 50,000, no more, in the book-version of the battle.

As for the movie, well, anything's possible in a movie so whatever you want.

And I don't think Sauron would have left the majority of his troops in Mordor, though the line

Hardly has our strength sufficed to beat off the first great assault. The next will be greater.

begs to differ.