Do upper arms need to be covered as tzniut? Males or females?
For men, there is no obligation to cover the upper arm. Indeed, in the hot summer days Rav Moshe Feinstein wore a short sleeved shirt that left part of the upper arm uncovered, and of course there is no problem with this.
For women, the upper arm is considered a “covered area” of the body, and must be covered, as the Mishnah Berurah rules (75:2).
This is also the common custom among observant Jews.