How many duty uniforms do active duty soldiers usually have on hand?

I had seven pairs. My job varied though; sometimes I wouldn't go through so many uniforms but then sometimes there were details, duties, or exercises that would soil uniforms rather quickly. I did try to wear uniforms at least twice before tossing them in the hamper though; washing them too often would wear out that stupid velcro too fast. I also had one uniform that I only wore for ceremonies or certain activities that I should look clean and presentable for.

IMO you will want four to seven sets of work uniforms. Normally one full service dress with one extra long sleeve shirt, one short sleeve shirt and one extra pair of pants. If your duty happens to require wearing service dress or class B every day (probably rare these days) then increase service uniform shirts and cut work uniforms to 3 or 4.

"Duty uniform," was a somewhat general term....I had "inspection uniforms (for muster and off the ship),"working uniforms (which may have some stains or dings in them (rendering them unfit for inspections))," and "dirty (or cruddy) uniforms (barely identifiable as a uniform (grease, tears, size). Normal routine on ship was to get your working assignment for the day this would determine which you wore for working hours. Slushing boat cables (greasing the davits) would kill a set of uniforms so dirties, going to the boat workshop on base was duty uniforms (because you were representing the ship and yourself), etc.. I had the required number of duty uniforms; but had at least two each of the others, plus of course dress uniforms of those sorts. In the course of your service your will "grow' those by simple use, and get rid of them when they no are longer serviceable.