Same font size for lyrics and markup

[Nora Widdecke]

Hi,

I have a score of a song with one line of lyrics and the remaining 
stanzas as markup below. Now I'd like the font size of the lyrics to be 
the same as the font size of the markup text.
I tried using

\override LyricText.font-size = #someNumber

but that applies someNumber as a factor, not as an absolute value,so I 
cannot assign the same value to the markup.

So how do I assign an absolute value to LyricText.font-size?
And if that doesn't work, is there any other way to make my lyrics and 
markup the same size?

Thanks,
Nora