Republic Commando: Hard Contact states that 10 droids plus a captain is a platoon. But this does not fit either with what we know or mathematically with what is seen in The Phantom Menace. One possibility is that this is but a part of a platoon – that the captain and an escort were accompanying a squad of 9 droids. The rest of the platoon would be committed elsewhere. This matches what we see in The Phantom Menace, 8 droids and a commander are sent to confirm the deaths of the Jedi aboard the SS Profiteer. We see more small units when the leaders of the Trade Federation depart their shuttle, but unfortunately the foreground prevents an accurate count. Since squads of 8 and an NCO appear to be the case then there could be 3 squads in a platoon, and 4 platoons in a company, fitting with observed evidence. There is a problem with the officer corps organization however, as the rank of Lieutenant was also stated in Republic Commando: Hard Contact. Possibly Major Hokan was given a higher rank then the unnamed captain because of his greater experience and they wanted to enforce the chain of command. This would allow for the officer ranks to fit, but it brings into question why the commander of a company was out on patrol with a squad while lower ranking officers were back at base. This requires further investigation, but the information needed is lacking.
On Zaarja we see formations of 24 by 19 marching over the hills for a total of 456. (Clone Wars: On the Fields of Battle) If this were including the officers, this would correspond to the expected strength of a battalion, which is 4 times the strength of the companies we saw deployed on the plains of Naboo.
Marching into Theed in The Phantom Menace we see each tank escorted by two formations of 20. This does not appear to match any known organization, but if the total size of the unit is unseen, it could work. If we counted the 4 droids inside each tank as attached to the unit (as we know that officers lead from tanks, as we see later in the film) that would make each unit number 44. If a regiment consisted of 4 battalions and a command staff of 24 this would fit, as 44 goes into 1,848 forty two times.
From this fragmented evidence we are able to piece together the start of an order of battle.
Squad – 8 droids + Sergeant, 9 total
Platoon – 27 droids + a lieutenant (3 squads), 28 total
Company – 112 droids + a captain (4 platoons), 113 total
Battalion – 452 droids + 4 command staff (4 companies), 456 total
Regiment - 1,824 droids + 24 command staff (4 battalions), 1,848 total
It is interesting to note that despite the fact that a squad is bigger, the rest of the units are significantly smaller then their Republic counterparts. Hopefully further information will be released, allowing us to detail a full order of battle for the Confederate Droid Army.