The Emperor Protects
For a while i've wondered what the exact size of the legions were before the Heresy. Some said around 10,000, where as others have gone much higher. But none of the Heresy novels had given an exact figure. But i listened to Ravens Flight today and Corax says he came to Istvaan with 80,000 marines. Now we know he left a company back at Deliverance and then theirs the Marines who would be spread out across the galaxy on various tasks. So i imagine we can safely assume the Raven Guard numbered at around 100,000. Dont ever recall hearing that Raven Guard were a large Legion, so if we take this to be an average, whats the conservative estimate on the size of the Ultramarines, who were meant to be vastly larger than most other Legions.