On the Web, vertical rhythm is contributed to by three factors: font size, line height and margin or padding. All of these factors must calculated with care in order that the rhythm is maintained.
“ The grid system is an aid, not a guarantee.
It permits a number of possible uses and each
designer can look for a solution appropriate to his
personal style. But one must learn how to use the
grid; it is an art that requires practice. ”
The ultimate resource
in grid systems.