Recently, my cp’s (critique partners) and I were discussing picture book story boards. There are two main types and it is confusing at first but hopefully this will make it more clear. The math for the number of pages is always divisible by four. One sheet of paper has two sides. Folding it in half creates four pages.
Both examples are of a tall picture book, but some picture books are square shaped while others are wide format.
For the 40 page self-ended storyboard, page one starts on the endpaper that is pasted down onto the board of the cover. This is how the inside pages attaches to the cover. In this version the story begins on pages 6-7 and has 16 spreads.
For the 32 page storyboard, page one starts on the title page. In this version the story begins on pages 4-5 and has 14 1/2 spreads.
IT FELL FROM THE SKY by the award-winning Fan Brothers is a whopping 52-page self ended picture book.