I wonder if the "boxes" aren't actually framed squares that have been cut in half.
If I were looking at it, the big block is 12", the other block is actually a four patch of blocks, the biggest of which is six inches, which would make the smaller ones to finish at three inches ...
nope, that isn't correct .... Bobbinwinder's numbers are good ...
I didn't see that set of blocks that went with the big block.
It sure is an attractive quilt! <wave>