Dimensions in pixels of a draw Area to obtain a plot on a A4 paper

[arkkimede <arkkimede gmail com>]

HI!
I've realized an App with GTK3 and the library CAIRO to plot results of
measurements.
I use the function "cairo_surface_write_to_png" to obtain a png file that I
put on a paper of format A4 (with usual resolution of 300dpi) to generate
reports.
Consider also that preliminary plot are observed on a screen with
resolution 1920x1080.

The question is:

Could you advice me dimensions in pixels of the draw area in order to
obtain png file to plot on A4 paper and see (more or less) similar pictures
on the screen
(or different dimensions for the plot on png and dimensions for the plot on
screen)?

Thank you