How many clone troopers were in the Clone Wars?

Archiving sources report a readiness of 3 million units. Units could refer to individual clones, battalions, or even armies! However, I prefer the battalion explanation, which would account for over one and a half a billion clones.
And yes, there were originally 200,000 clones on the battle of geonosis, and 1,000,000 more in their final stages of training at that time. (individual clones, not units this time). However, the numerically superior droid army forced the increased production of more and more clones.
Many times were military forces increased, including one well known time where 1000 acclamators were ordered. That's why military forces would have to increase with crew increase. (Seriously, the crew of destroyed ships wouldn't realistically be salvaged, so new crew members needed to be grown.)
The clones were grown on Kamino, which is a planet in it's own right. Population of Coruscant was (unrealistically) a trillion, so then assuming that, Kamino being a planet would have a very large population of clones, the population of a typical planet! being somewhere in the billions. Centax was also a clone factory (but it was secret). It's a moon though, so production was probably less.
And there were 10,000 Jedi. each Jedi is a General, and usually, generals command armies, and armies are usually around 100,000-200,000 strong. multiplying 10,000 by 100,000 to 200,000 gives us 1 billion to 2 billion, which is the number I previously gave, in where battalions are units.

But that's the beauty of fiction, where you're allowed to draw your own conclusions where specifics are uncertain!