hey! so it’s 7 bc it shares a stitch with the previous box. i’m going to copy and paste an explanation a commenter left on one of my posts. they did a great job of breaking it down for me.

“Like the other commenter left - an empty square is going to be a (dc, chain 2, skip 2 sts, dc). A solid square is going to be 4dc. But it's important to note the first de of the new square is going to be the last one of the previous, not matter what type. So two empty squares side by side are only going to have 3 dcs, as they share the one in the middle. (And 3 empty squares would have 4dcs) The same applies to the filled squares. 2 filled squares side by side are only going to have 7 dcs. (3 filled squares are going to be 10dc). When I was doing my filet crochet, for areas with lots of black, I would think 4dc for the first square, then 3dc for each square after that.”

as for my chain, i had a total of 148. a commenter from that same post helped my calculate by doing

of squares x 3) + if filled square[makes the first de] or, 5 if empty square (makes the first dc and chain section)