KOMA Script footer line height

try this:

\documentclass[]{scrartcl}
\usepackage{calc}
\usepackage[headsepline,footsepline]{scrpage2}
\clearscrheadings
\ihead{Header}
\ifoot{\rule{0pt}{\ht\strutbox+\dp\strutbox}Footer}
\pagestyle{scrheadings}
\begin{document}
\mbox{}
\end{document}