Best main text, font-size for responsive css design ?
 

My last sites, have been designed with responsive css. I make use of media queries.
When I check them in some smart phones, the text was not very readable, due to font-size.

I normal use 12-13px font-size for the main text
. I think that is not a good approach. What is the best font-size for all ???
In percentage (%) or in ems. And what size ??

normaly use 16px font-size for the main text. I think that is a good approach. I think this is the best size for media queries.

Font size 14 px is a average for all site content, and also use a san-serif ,it make a site to attractively