If you're gonna use shams on your king size bed then the amount of shams you need for the king sized bed is between 3 to 4 shams.
The size of the shams can make a difference as well in the amount of shams you need for your king size bed.
But figure on 3 to 4 shams to fill and fit the king size bed.
To figure out the exact amount of shams you need for your king size bed take the size of the shams and then measure your bed and that will give you the exact amount of shams for your bed.
If you get too large of shams then they can overhang the sides of the bed a little and that will be okay.
But usually 3 to 4 shams will be enough to complete the king bed.