I didn’t measure or calculate, I just worked from an idea. I cut a bunch of one inch squares from the scraps of fabric I used for the yo-yos. I attached them in twos along the diagonal, cut off the extra, and pressed them open to make new squares.
I stitched the little squares together in a line and cut a rectangle from the sleeve of a black kimono for the body of the holder. Can you see the geometric pattern in the black fabric? Next, I made a slice down the kimono fabric, but not in the center, and inserted the strip of squares.
I lined it with some fabric from my stash and folded about a third of it up. Next, I twisted three strands of #8 perle cotton into a thin cording and stitched it along the edges.