How does a 1000 mcg pill compare to a 600 mg pill?

Answer 1

1000 mcg = 1 mg.

So a 600 mg pill has the active ingrediant of 600 1000mcg pills.

That is the math. But do not substitute pills for each other without consulting a doctor or pharmacist. That could be very dangerous and even cost you your life. For example. the coating on a pill, particularly a time-release pill, could make a huge difference in how a pill works if you try to split it or if you try to take several smaller pills instead of one large pill.