The former Buffy The Vampire Slayer star and husband Prinze welcomed daughter Charlotte Grace in September.
Speaking to People, Gellar said: "We both wanted something that was traditional but that you didn't hear every day. I was one of four Sarahs in my class growing up.
"It was, for us, about looking for something that fit into that classical vein but was still special."
Prinze added: "It's almost weirder for her to be called Charlotte. She's going to be in school with a Magic Appleseed, or something, and it's going to be weird that she's Charlotte.