Checkers anyone?

My Grandson gave me a cookie from a piece of tree he found, and asked me to make a checker board out of it.  I used a router sled to flatten it.  I placed blue painter tape on it so I could mark out the biggest square I could make on it.  It turns out to be a 10 inch by 10 inch square.  Now I am trying to figure out how big the squares need to be in order to make the checker board.   

I did a Google search and found a lot of quilting patterns.  Is there a simple way to do the math?

Thanks
Mike