Not every lady wants big. An insecure guy would hear this question one way, like “do you have a small dick or what?” But it could also mean “are you going to hurt me because you’re too big?”

All of that assumes she has some interest in you. If it’s just a random person asking another random person then “that’s none of your damn business” would apply.

Everyone here’s saying “one way to find out WINK WINK” but that assumes she’s someone you want to have sex with. In my life the only women I’ve met who were this crass and forward were also beasts I wanted nothing to do with.