To check for doneness, the internal temperature should be 125 to 160 degrees F depending on your desired doneness. Rare burgers should be 125 degrees F and they will be reddish-pink inside. Medium rare is 135 degrees F and mostly pink. They should be 145 degrees F and partially brown for medium doneness. For medium-well burgers, your thermometer will read 155 degrees F and the middle will be mostly brown with a little pink. And well-done burgers will be 160 degrees F with no pink at all.