Somebody check my math, but here is what I came up with:
The HST height and width is 6.5 stripes. If stripes are 1.25", then the HST is 8.125" (8 and 1/8). The stars are 6 stripes high, and 8 stripes wide, so that piece is 7.5 x 10.0. The long stripes are the same as 3 HST, so those are 24.375 (24 and 3/8). The short stripes are 24.375 - 10 = 14.375. If you add a 6" border, that puts your finished quilt at ~ 61 x 85, so you'd use a twin size batting. These are all finished sizes so you have to add seam allowance.
If you want it a bit smaller (and also avoid the 1/8" measurements) your finished stripes are 1" wide, HST is 6.5", stars are 6 x 8, long stripes are 19.5", and short stripes are 11.5".
Someone please check me as I am not a morning person!
Darren