Not necessarily a pattern question

Ok, i have this friend who wants me to make her a pair of socks. She says she wears a U.S. size 9.5 shoe but a 10 inch sock.

Is she referring to (sock) foot length, like how long I should make her sock foot?

Or is she referring to sock circumferance?

Please help!

The only way to know for sure is ask her.

I know that, but it is a surprise and I do not want to ruin it.

Storebought socks are usually measured as the length of the foot I think, so 10" sounds about right.