Most Tolkien scholars estimate the size of Sauron's forces at somewhere around 200,000 orcs, Easterlings, and men of the Horadrim, although it's worth noting that Tolkien didn't provide concrete answers.
The Roman legions at their height (Emperors Trajan and Hadrian) numbered between 400,000 and 450,000 legionaries and auxilia.
Not decisive, but 2:1 are decent odds.
It's worth remembering that Tolkien was specifically writing to reflect the cultural makeup of Anglo-Saxon England, where 10,000 men would be considered a massive army. If he had been writing to reflect the Roman era, he may well have revised the numbers upward.