I say its 12” as that is what the pattern should work out to, but with 8ply yarn and a 4mm hook its finished size is 19cm. Not keen in adding heaps of rows to make it up to 12” (30cm)
So the plan for this CAL is 30 x 12” blocks (19cm blocks) thats 2 from the CAL choices and a third every 2nd month or so from my own choices.