Well BUB get a smaller Mug that's less than 3 3/8 inches diameter on the bottom,,, My big mugs just do not fit. You have to use a disappointingly woosy smaller one; Some bitsy Fem teacup barely containing two gulps of brew. Try to find a mug with a flat bottom to transfer the heat better. Come on Sunbeam make a MAN sizes MUG warmer!!!!