Here is another of the folded log cabin blocks. They are quite dense and heavy for their size, which is approximately 7.5 inches. Yet another:
By the way, these blocks are supposed to be 7.5 inches unfinished, but no two are exactly the same size. They have not been squared up, or as Bonnie Hunter says, squared down. You can't add fabric, only remove in the squaring process. They may need one or more strips added to bring them up to sufficient size to trim down to 7.5 inches.