2nd place: South Korea, 7.2 million people.
3rd Vietnam 5.5 million people
4th place India
5th place Russia
Of course, this is meaningless because it is a combination of active duty + reserve forces + various strange paramilitary organizations such as the Civil Defense, Worker-Peasant Red Guards, and Boy Guards.
The size of the South Korean reserve force is simply the sum of the number of people who can be called up in wartime. Not all of these people will be called up, and just as civil defense is not a meaningful force, the same is true for North Korea and Vietnam.
The ranking of active-duty military forces is naturally India, China, and the United States.