How to change font size of footnotesize to 11pt?
By using renewcommand the size of footnotesize could be changed. For example if normalsize is 12pt and you want 11pt for footnotesize just \renewcommand{\footnotesize}{\small}.
\documentclass[12pt]{article} \begin{document} \noindent Just a dummy text\footnote{more senseless text in 10pt}.\\ \noindent \renewcommand{\footnotesize}{\small} Just a dummy text\footnote{more senseless text now in 11pt}. \end{document}