Geese are always twice as wide as they are tall. So if you know the finished width you want, then your strip is that wide plus 1/2". And the height is half of the finished width, plus 1/2. The squares to make the "sky" are the same size as the height of the strip.
So, for example, if your finished strip is 4" wide, then you have
strip - 4.5" x 2.5" (to finish at 4x2)
squares - 2.5" (2 of them)