Sans is a short and big-boned skeleton, wearing a hoodie or simple jacket, unzipped at all times, with a white shirt, black shorts and sneakers.
He is seen with a grin at all times, and only moves the corners of his mouth at certain scenes. He has white pupils, which tend to disappear when he is serious. A bright, flashing iris appears in his left eye socket during the battle against him, as well. This eye starts off merely glowing, but as he utilizes his time warping powers, it starts to flash.