Calvin is 11 years old. He has blond hair, dark green eyes and has freckles on his face. Usually he is seen with an orange plaid shirt and brown shorts, but when the boy goes to play with his twin brother Sam, he dresses in his astronaut costume, while Sam dresses as a soldier. He has an older sister named Molly, the second oldest Barbara, his twin brother Sam and the youngest of all Walter. Her mother is named Edie and her father Sven. Calvin uses they/them on whoever is talking to him.