Since the Twister tools have become so popular and so many projects have been photographed and shown on QB, many of us are making up our own designs from looking at what others have done.
Made up a design (or perhaps copied someone else's idea from years ago) with my new twister tool -- to make place mats using the midi-twister (6 1/2" blocks). The mats come in at 18 1/2 x 13 3/4" (before quilting/binding) -- BUT -- the sewn squares create a sheet of fabric ready to be cut by the tool which is 30 x 24" (4 x 5 blocks).
Getting ready to teach this as a class at my LQS -- did manage to cut down on the fabric requirements a bit by using border strips all the way around which are 6 1/2 x 4 1/2" -- this could be cut down a bit more by experienced folks, wanted the students to have some leeway.
When I plan now to use my twister tool, after making up the design or working with one already pictured like yours (which is STUNNING by the way), I count the number of blocks in the photograph and instead of multiplying that by my 6" (after seams) block, I use 3 3/4" which is about the size of the finished block after using the tool. This is not an exact amount -- rounded up a little, as if you do the math, my seams are like so many others, not quite all perfect!
You can figure the numbers for the big twister and the mini also! And use those as your guide.
This might help others as they get ready to use their twister tools for Xmas projects. Some tools use more fabric than expected but the time you save in using the tool justifies this, and the pattern is one which you like.