From canon quotes the Republic’s total forces can have initially numbered no less then 8.4 million. Other sources indicate it would have numbered in the dozens of billions from the onset, with extrapolated figures giving a strength of at least the tens to hundreds of quadrillions (10^16 – 10^17), consisting of 1.2 million Advanced Recon Commandos, 3 million clones of varying rates secretly trained to answer only to Lord Sidious, the Republic Commandos numbering between 100 million and 2 billion, tens of billions serving as pilots and spacemen in the space combat branches, and the infantry and specialists making up the difference, with trillions serving only as law enforcement at the end of the war.
Meanwhile the total strength of the Confederate Droid Army canonically cannot be less then several billion, with other canon figures stating numbers in the quintillions (10^18). Of this, quadrillions (10^15-10^17) make up the infantry fighting forces with B-1 type Battle Droids serving as infantry and specialists, and B-2 type “Super Battle Droids” and Droidekas serving as heavy infantry. Each of the vehicle classes would number in the billions, and remaining difference being navy crews, supply, and construction droids. But with the execution of the Confederate leadership, the clones outpaced the droids to become the standard for the new Galactic Empire.