Using Pythagorean Theorem to find perimeter, or THOSE TERRIBLE TINY SQUARES!

I am trying to do the Pythagorean theorem to find perimeter exercise in basic geometry.  First, there is not a video on KA, but I did find on Youtube.  

Secondly, I need some instruction on how to count THOSE TERRIBLE TINY SQUARES!  The line does diagonally through these, how do I count?  Is there any way you could change the format (get rid of THOSE TERRIBLE TINY SQUARES), and give the exercise another way?  Please!  Pretty please!  With a cherry on top!? 

Thank you in advance.

Jennifer in AZ