Reduce populations by 99.9%, otherwise the population is so freaking large, it takes every army in the inner sphere combined to garrison it.
Dropping those populations means you can take modern percentages of military (.5% for US) as a good guide.
Lets say a planet with 3B people, that is 3M when reduced 99.9%. .5% is 15,000. That is about 20 infantry regiments for a country like the US, though Israel with its 24% military is like 970 regiments at that ratio!
The city of Dallas is 1.9M people, and 3121 cops. Basically 4 regiments of police officers, and with 20% civilians fit for service, up to about 500 regiments of militia, for just 1.9M folk.
If even 1% of the people are disgruntled enough to riot, they outnumber cops. If 2% or more are, they significantly outnumber the cops. If 2% of those fit for service decide to take arms and fight, that is 10 regiments of green infantry armed with bolt action rifles, and perhaps inferno grenades (molotav cocktails).
If you stick with the printed populations, your talking tens or hundreds of thousands of regiments, even if you say only 1 in 10 soldiers is a "fighter", and the rest are support.