The smaller twister tool (the one that you would use with 5" squares) is 3.5", so the cut blocks finish at 3". The tool is positioned on the seam between the charms. So if you have 2 charms, you can cut 1 twister. If you have 3 blocks you can cut 2 twisters. In other words, you can cut 1 less than the number of blocks you have joined.
So if you start with 17 blocks, you can cut 16 twister blocks that finish at 3", yielding a 48" quilt. Note that if you add a border before you cut, this counts as a block on each end. the borders can be cut smaller than the 5" charms because the tool only cuts part of the starting and ending block.
You can apply the same calculation to the larger tool measure it (I think it's 6.5"), subtract the half inch seam allowance, and use that in the calculation.
Last edited by PaperPrincess; 09-27-2013 at 11:21 AM.