http://www.alistapart.com/articles/keepelementskidsinlinewithoffspring - Keeping Your Elements’ Kids in Line with Offspring
What happens when we declare the height and width of an element?
When we declare height and width of an element, we are declaring height and width of its content area (its inner height and width). This height and width does not include padding, border, and margin.
Does the background of an element includes its margin?
No. The background of an element includes its content area, its paddings, its borders, but not its margin.
How can we determine the true height of an element?
True height of an element is determined by: declared height + padding top + padding bottom + border top + border bottom
How can we determine the true width of an element?
True width of an element is determined by: declared width + padding right + padding left + border right + border left
For IE, without a doctype, does the declared height and width include paddings and borders?
Yes. IE (without a doctype), the declared height and width does include padding and border.