Latex: \headheight is too small

You never know what you will meet when you use Latex, luckily, we can search Google or Yahoo to find the answer. However, it cannot help all the times. There is a problem you may come across using package fancyhdr:

Package Fancyhdr Warning: \headheight is too small (12.0pt):
Make it at least 14.49998pt.
We now make it that large for the rest of the document.

It was not easy to find the answer via either Google or Yahoo. Here is the solution. Insert

\setlength{\headheight}{15pt}

in the preamble, i.e. before \begin{document}.

Tips:

• \headheight defines the height of the header.
  
  
• \setlength{len-cmd}{length}

The \setlength command is used to set the value of a length command, len-cmd, which is specified as the first argument. The length argument can be expressed in any terms of length LaTeX understands, i.e., inches (in), millimeters (mm), points (pt), etc.