I haven't made this quilt but I recently quilted one so I think I know which one it is. I'm not 100% guaranteeing my math, but here's what I come up with:
You need a total of 936 squares to get the finished size you want (26 x 36 = 936). Divided by 5 = 187 sets of 5 plus one left over. (187 x 5 = 935 + 1 = 936).
If you subtract off the '24 sets of four plus 24 singles' for the partial plus signs, that leaves 163 sets of 5 (187 - 24 = 163. I counted this as 24 full sets since 24 x 4 =96 + 24 = 120/5 = 24)
So:
163 x 5 = 815
24 x 4 = 96
24 x 1 = 24
815 + 96 + 24 = 935
Okay, I'm off by one. So you may need one extra 'onesie'. Personally, I'd cut an extra set of 5, because it may depend on how you start the row whether you have a full or partial 'plus sign'.
Or just cut about 936 EXTRA squares, piece those together too, and then you can send the extra top to me!!
Andi