Reference HTML Cheatsheet
HTML has six levels of headings, numbered 1 through 6, with 1 being the most prominent. Headings are displayed in larger and/or bolder fonts than normal body text. The first heading in each document should be tagged <H1>.
The syntax of the heading element is:
<Hy>Text of heading </Hy>
where y is a number between 1 and 6 specifying the level of the heading.
Do not skip levels of headings in your document. For example, don't start with a level-one heading (<H1>) and then next use a level-three (<H3>) heading.
Header Size 1
Header Size 2
Header Size 3
Header Size 4
Header Size 5
Header Size 6