Sub Articulo 39.0

I hope someone can help me out with the following questions:
1. I have a variant of book.sty where the normal font is 10/14. My headings
are 12/17. Now, if I want the total vertical space of the space above the
heading + the heading itself + space below the heading to be equal to the
height of two normal rows of text, should I take space above = 9pt and space
below = 2pt (i.e., 9 + 17 + 2 = 28) or space above = 12pt and space below =
4pt (i.e., 12 + 12 + 4 = 28)? (So, my problem is that I don't know if the
vertical height of a heading, on a single row, equals the font size or the
baselineskip.)