How to calculate these rectangles for more precises movement? (Beginner/Noob question)

I am trying to make the rectangles on this https://www.dropbox.com/s/emovsg1h12knhav/Person%201.jpg?m guy more precise for better collisions. Instead of him being 1 big rectangle, I want to make him into 3 smaller ones. (Rectangles in pink are what im trying to measure) How would I measure them and add them accordingly into this code? I was told to measure the corners and change the code depending on the amount of pixels but I am confused.  Sorry I am a noob.

            personRec1 = new Rectangle(620, 380, 75, 75);
            personRec2 = new Rectangle(620, 380, 75, 75);
            personRec3 = new Rectangle(620, 380, 75, 75);