A reg. king is 76x80 and a cal. king is 72x84. The big question is what is the depth of the mattress. If the mattress is say 15" thick then add 30" to 76" then 2-3" for each side it to go below the top mattress.
So 76+30+4= 110 wide
Now Do you want the quilt to go over just the top of the pillows or tuck in? I probably would do 80" + 15" + 2" = 97" for under pillows. I probably would add 6" to that # if to go over the pillows and if tucked I would add the additional 15".
So tucked would be 80+15+2+15= 112
110x112
this comes out to 110x110