Personally I just take a look at US military numbers and multiply them with a percentage (so I am effectively dividing it).
The ratio would depend on many factors.
For example drone weapons would be actually more numerous in Neo Hungaria than what the US currently has because we are in the future. Yet actual aircraft numbers are about the third of US.
Same with the rest. For example I compare my population to current USA and use that ratio for the number of my troops.
I compare to the USA because Neo Hungaria spends similar amount on defense.
You can take other nations's militaries as an example if those fit your nation's style more.
I wouldn't advise Germany though because those numbers are the results of long periods of peace, not something we have here.