How to calculate x y coordinances

When you place an item or destination square, the numbers that appear below the box are the x y coordinates.

What I was sorta talking about was figuring on a screen basis to fill in the freeform combos with.
I guess from what you're saying I can go a tile by tile and write them down.

I was thinking about setting up one of those fire rings that were in LTTP

all X and Y values are bsed on pixels.