While KFC's official site lists the ingredients in their coleslaw, they do not list the measurements. However, some copycat recipes are available, one of which is from chef Todd Wilbur in his book "Top Secret Recipes".
Todd's recipe combines 1/2 cup mayonnaise, 1/3 cup sugar, 1/4 cup milk, 1/4 cup buttermilk, 2 1/2 tablespoons lemon juice, 1 1/2 tablespoons vinegar, 1/2 teaspoon salt and 1/8 teaspoon black pepper in a large bowl. Beat until smooth. Finely chop 1 head of cabbage and 1 medium carrot. Add 2 tablespoons of minced onion. Mix all ingredients together and refrigerate for two hours.