glPointSize to world coordinates circle radius

I'm looking for a method to draw sprites of a given radius. In order to change the dimension of a sprite I use glPointSize, but how can I convert the float I pass in to the shader to a radius in world coordinates?

In openGLES resources they say that glPointSize is the diameter of rasterized points, but I don't understand how can I convert this value to world coordinates.

I'm using Java + openGLES 2.0 on Android