How to change the fontsize in beamer_presentation smaller?

Question

I want to make the font size of code Chunk in R markdown smaller so that each slide can contain more content.

I tried to set the font size for the total beamer,

title: "In"
author: "Y"
output: beamer_presentation
font_adjustment: -2

But even I changed "font_adjustment = -2 " to "-15", there seems no changes to the font size.

Answer 1

I just found the answer,

fontsize:  12 pt

Thanks.