\settoheight{len-cmd}{text}
The \settoheight command sets the value of a length command, len-cmd, which is specified as the first argument, equal to the maximum height of the text argument in the current font.
For example,
\settoheight{\baselineskip}{Xanadu}
\setlength{\baselineskip}{1.5\baselineskip}
would set the value of \baselineskip to 1.5 times the height of the capital "X".
See Lengths