While "bras" can refer to the whole arm, it specifically translates to "upper arm" when the context makes it clear.
For example:
* "J'ai mal au bras." (I have a pain in my upper arm.)
* "Le muscle du bras est très fort." (The upper arm muscle is very strong.)
You could also use "le haut du bras" to be more specific, meaning "the top of the arm."