The angle and the narrow-ness of the tail would look like a male to me. There are a pair of tiny grabber legs underneath the area between the body and tail. Females will have a wider space underneath the tail for holding eggs/ developing babies.
If you have the opportunity to watch a bunch of them in a tank (like at the fish store) you will start to see the angle is more narrow part, especially towards the end of the tail where the end/rounded fan part of the tail is (it is called a telson - had to look that up!). But it is easier to see a bunch of them to more easily distinguish the shape difference. The pleopods are also called swimmeretes, in the females they hold and fan the eggs are larger, slightly more rounded to the tail fan from what I noticed.
If it is very small/young (like a half inch) you may not be able to tell till it's further developed.