A King sized mattress is 76 x 80 (w x l). If you want a 10 inch drop, then make it 96 x 90. (Adds 10 inches to each side and 10 inches at the foot. If you want a 10 inch tuck under the pillows, make it 96 x 100 (Adds 10 inches to each side and 10 inches at the foot plus up to 10 inches to tuck under the pillows.) Other sizes of drop and tuck (sounds like fire prevention, doesn't it?) can be computed in the same way. the 104 x 104 mentioned above gives you a king with 14 inch drop and 10 inch tuck. God bless you, I've never had the courage to take on such a big quilt!