So what is the actual size of the Grand Army of the Republic? There are a number of references that we could consult to reach an order of magnitude estimate. While Attack of the Clones states that 1.2 million “units” have been produced, “unit” is never defined beyond Master Kenobi’s assumption that 1 unit equals 1 clone (Attack of the Clones novel). In fact, later in the film when General Windu parts company with General Yoda on Geonosis, he is told there are 5 commando units waiting for him. He is then joined by 6 clone troopers and is seen running toward another group of 6. This suggests that a unit is equal to seven clones (6 troops and one leader), a fact examined in more depth in the Organization section. It also provides a minimum "G-canon" strength of at least 8.4 million clones. In looking at the deployment scene at the end of Attack of the Clones estimates rage to several million troops being deployed from Coruscant. That the “Republic’s best military historians and theorists” (Guide to the Grand Army of the Republic) would pull all their troops back from Wild Space to the Core worlds only to send them back to the Outer Rim again is illogical to say the least. We know that new clone production centers have been built on Coruscant (Odds) and it is possible these are their products. This is much more favorable as the time to make a clone trooper (as opposed to ARC trooper or Clone Commando) is unknown but less then several years (estimated at ~ one month in the Production section) and the time from the battle of Geonosis to that scene is unknown, and stated only to be shortly after the battle of Geonosis. (Republic Commando: Triple Zero)
The Guide to the Grand Army of the Republic states a total of 3 million clones. However, this contradicts other sources, including Attack of the Clones. But it also says that these forces answer to the Supreme Chancellor, and we know that is not the case – until the Senate amended the constitution giving Lord Sidious complete control over the Jedi Order the Jedi and the Grand Army of the Republic answered to the Senate, not the office of the Chancellor. (Revenge of the Sith novel) It is possible that the 3 million the Guide to the Grand Army of the Republic describes refers only to specific units based out of Coruscant like the 501st Legion or Shock Troopers (Revenge of the Sith Visual Dictionary), who underwent special training and conditioning on Coruscant. (Star Wars Databank – 501st legion) That the Order of Battle provided says Jedi also commanded these units is not a contradiction – having clones loyal to him commanded by important generals aids his eventual plan of the destruction of the Jedi Order; the fact that Lord Sidious addressed unit 2224 AKA "Cody" by name would support this interpretation. We further know that units such as the 501st first saw action at Geonosis.
General Yoda deployed 192,000 clone troopers on the battlefield at Geonosis (Star Wars: Complete Locations), with an unknown amount serving as crew aboard the Acclamators that landed or the “thousands” of Republic ships attacking the Confederate fleet in orbit (Attack of the Clones novel). The ability to mobilize on such a short notice (a matter of hours or less) would indicate that the statement “Tipoca is already primed to deliver 200,000 clone troops” refers to the surge ready clones, not the total number. (Star Wars: Complete Locations) That interpretation also matches the statement in The New Essential Chronology that it took time to activate the clone army, not that it took time to build it. A large number of casualties were suffered at Geonosis; reports on the ships incoming to Ord Mantell listed as receiving 12,000 in need of triage, 8,000 walking wounded, and 72,000 combat fit troops (Republic Commando: Hard Contact), and General Grievous personally killed “entire clone trooper companies” or at least 288 trooper plus officers according to Unknown Soldier: The Story of General Grievous. The 100,000 missing troops in the Ord Mantell report indicates that either multiple bases were used, that 100,000 is considered an appropriate garrison force (Star Wars: Complete Locations), or that the Grand Army suffered over 50% casualties in its first victory. The Star Wars Roleplaying Game Revised Core Rulebook states that the Republic immediately ordered 1,000 more Acclamators indicating an army of at least 16 million. Star Wars: Complete Locations says “The first batch of clone divisions are ready for deployment; millions more are undergoing intensive performance evaluations”, with the context being clear that the millions refer to divisions, not individual clones. To mesh between a corps and brigade a division would be 18,432 troops, thus the Grand Army of the Republic would have a minimum starting number of 36.9 billion.
A common number used in early literature was 1.2 million, being based out of Master Kenobi’s interpretation of Lama Su’s statements in the Attack of the Clones novel. This fails when compared with other sources set at the same time and later however – Labyrinth of Evil states only half of the initial 1.2 million clones remain, but the Revenge of the Sith Visual Dictionary states three quarters of the initial army remains. This is inherently contradictory, and must be rationalized. One possibility is that the 1.2 million figures refer only to ARC troopers – General Kenobi is referring to a squad of ARCs when he thinks the above statement in Labyrinth of Evil. Such an interpretation would also fit Shatterpoint and The Cestus Deception, where General Windu talks about 1.2 million troopers being insufficient to train civilians (Shatterpoint) and the fact that ARCs are specifically trained to recruit and train civilians to act as troops and insurgents (The Cestus Deception). This would also fit with The New Essential Chronology without contradicting other sources; The New Essential Chronology states that an initial 200,000 clones were deployed with an additional 1 million being deployed only after the battle of Kamino. Since ARCs are known to have been deployed at Geonosis (Republic Commando: Triple Zero) and a large number of them removed from stasis for the defense of the Kamino (Clone Wars: The Defense of Kamino) this would fit. This is not to say all the clones participating in the battle of Geonosis are ARC troopers, as we know that was not the case, but this solution allows for a rationalization of most of the evidence. There is the problem of how Jango was able to train 1.2 million clones, a solution there would be that he only trained the 100 “Alpha” series clones (Guide to the Grand Army of the Republic; Geonosis and the Outer Rim Worlds), and that others trained the rest. This is supported by the fact that we know not all ARCs were trained by Jango; Sergeant Skirata trained the Null series ARCs. (Republic Commando: Triple Zero)