Eric Eggert, Knowbility/W3C/WAI
The size of the target for pointer inputs is at least 44 by 44 CSS pixels except when:
Equivalent: The target is available through an equivalent link or control on the same page that is at least 44 by 44 CSS pixels;
Inline: The target is in a sentence or block of text;
User Agent Control: The size of the target is determined by the user agent and is not modified by the author;
Essential: A particular presentation of the target is essential to the information being conveyed.